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ESSENTIALS    OF    BIOLOGY 

PRESENTED  IN   PROBLEMS 


BY 
GEORGE   WILLIAM   HUNTER,   A.M. 

Head  of  the  Department  of  Biology,  De  Witt  Clinton  High 
School,  New  York 


NEW   YORK  ••.CINCINNATI   :.  CHICAGO 

AMERICAN    BOOK    COMPANY 


COPYKIOHT,    1911,   BT 

GEORGE  WILLIAM   HUNTER. 

Entered  at  Stationers'  Hall,  London. 


mrNTBB.    essentials  of  biology. 
W.P.I 


THE   PLAN   AND   PURPOSE   OF   THIS   BOOK 

The  plan  of  this  book  recognizes  first-year  biology  as  a  science 
founded  upon  certain  underlying  and  basic  principles.  These  prin- 
ciples underlie  not  only  biology,  but  also  organized  society.  The 
culmination  of  such  an  elementary  course  is  avowedly  the  under- 
standing of  man,  and  the  principles  which  hold  together  such  a 
course  should  be  chiefly  physiological.  The  functions  of  all  living 
things,  plant  or  animal,  movement,  irritability,  nutrition,  respira- 
tion, excretion,  and  reproduction ;  the  interrelation  of  plants  and 
animals  and  their  economic  relations,  all  these  as  they  relate  to 
man  should  enter  into  a  course  in  elementary  biology. 

But  to  make  plain  these  physiological  processes,  difficult  even 
for  an  advanced  student  of  biology  to  comprehend,  the  simplest 
method  of  demonstration  is  necessary.  Plant  physiology,  because 
of  the  ease  with  which  simple  demonstrations  can  be  made,  is 
more  profitable  ground  for  beginners  than  is  the  physiology  of 
animals.  The  foods  which  animals  use  are  manufactured  and 
used  by  green  plants;  the  action  of  the  digestive  enzymes,  the 
principle  of  osmosis,  and  the  subject  of  reproduction  can  better 
be  first  handled  from  the  botanical  aspect.  The  topics  just  men- 
tioned introduced  from  the  standpoint  of  the  botanist  gain  much 
by  repetition  from  the  zoological  angle.  The  principles  of  physi- 
ology, after  being  applied  in  experiment  to  plants  and  animals, 
emerge  in  final  clarity  when  applied  at  the  last  to  man,  —  the 
most  complex  of  all  living  things. 

One  of  the  most  important  factors  in  successful  science  teaching 
is  repetition.  In  a  recent  address  President  Remsen  of  Johns 
Hopkins  University  said  :  — 

"  The  most  important  defect  in  the  teaching  of  chemistry  to-day  is  the 
absence  of  repetition.  There  are  too  many  fleeting  impressions.  We  cover 
too  much  ground.     The  student  gets  only  a  veneer." 

5 


6      PLAN  AND  PURPOSE  OF  THIS  BOOK 

What  is  true  of  chemistry  is  equally  true  of  biological  science.  We 
spend  too  much  time  in  teaching  unessentials  taken  from  our 
immense  field,  and  we  do  not  spend  enough  time  in  emphasizing 
from  constantly  varied  points  of  attack  the  fundamental  truths  on 
which  the  science  of  biology  is  built.  The  pages  which  follow  are 
an  attempt  to  drive  home  by  repetition,  and  from  many  points 
of  view,  some  of  the  important  principles  of  physiological  biology. 

One  sufficient  reason  for  the  placing  of  a  course  in  biology  in  the 
first  year  of  the  secondary  course  lies  in  the  fact  that  at  this  time 
the  child  is  receptive  to  the  message  of  applied  biology.  Private 
and  public  hygiene,  the  message  of  protective  medicine  and  san- 
itation, the  story  of  pure  milk  and  of  pure  water  and  what  they 
mean  to  a  community ;  all  these  things  can  most  logically  be  pre- 
sented in  a  course  that  makes  man  the  center.  The  allied  topics 
of  conservation  of  plant  and  animal  life,  the  destruction  of  harm- 
ful plants  and  animals,  the  relation  of  insects  and  other  animals  to 
the  spread  of  disease,  and  the  work  of  civic  and  government  de- 
partments in  the  development  of  nature's  gifts  and  in  the  preser- 
vation of  national  health  should  be  treated  in  their  relation  to 
man. 

Moreover,  the  data  given  should  be  treated  from  the  biological 
standpoint,  not  that  of  botany,  zoology,  or  human  physiology. 
Ideally,  we  might  take  up  general  principles  and  draw  from  the 
great  storehouses  of  plant,  animal,  and  human  biology  to  illustrate 
each  principle  before  going  on  to  the  next.  Practically,  however, 
such  a  plan  does  not  seem  to  be  workable,  partly  because  of  the 
difficulty  of  collecting  enough  material  to  make  such  demon- 
strations possible.  It  is  impracticable  with  immature  students, 
because  they  cannot  grasp  the  many-sidedness  of  the  application 
at  once.  This  will  only  come  after  repetition  of  the  principle,  each 
time  from  a  slightly  different  point  of  view. 

It  frequently  happens  that  the  related  study  of  plants  and  ani- 
mals may  be  taken  up  to  advantage.  Insects  and  flowers,  both 
plentiful  in  the  fall,  may  well  be  studied  together  for  the  relation 
of  life  habits  and  adaptations  in  the  insect  to  cross-pollination 
of  flowers.  Applied  biology,  in  its  relation  to  plants  or  to  animals, 
must  of  course  be  treated  from  all  sides.  The  fungi  and  the  bac- 
teria in  their  relations  to  man  are  conspicuous  examples. 


PLAN  AND  PURPOSE  OF  THIS  BOOK  7 

The  following  chapters  present  such  a  course  as  has  been  out- 
lined above.  Beginning  with  a  brief  treatment  of  the  constitution 
of  the  environment  of  plants  and  animals,  it  is  shown  that  both 
animals  and  plants  take  certain  materials  from  their  surroundings, 
and  that  they  may  be  profoundly  modified  by  the  factors  in  their 
environment.  The  flower  and  fruit,  together  with  the  related 
topic  of  insects  in  their  relation  to  flowers,  are  taken  up  in  the  fall 
when  material  is  abundant.  Reproduction  and  the  survival  of  cer- 
tain plants  because  of  their  adaptations  is  the  central  theme.  Con- 
siderable emphasis  is  placed  on  the  subject  of  fruits  useful  to  man, 
plant  breeding,  and  other  topics  of  economic  importance.  In  the 
study  of  the  seed  and  seedling,  the  external  factors  influencing 
growth  are  emphasized.  The  little  plant  within  the  seed  is  seen 
to  be  a  living  organism  that  breathes,  feeds,  and  grows.  Roots 
are  shown  to  be  absorbing  organs,  the  method  of  osmosis  being 
explained  in  detail.  The  subject  of  soils  and  the  relation  of 
bacteria  to  crop  rotation  is  taken  up  at  this  point.  A  discussion 
of  the  stem  introduces  the  idea  of  transportation  of  material. 
The  leaf  serves  to  introduce  the  pupil  to  plants  as  food  and 
oxygen  makers.  Forestry  is  developed  at  this  time,  consider- 
able emphasis  being  placed  on  the  need  for  conservation.  Then 
follows  a  discussion  of  plants  of  various  forms,  of  the  simplest  of 
plants,  and  particularly  with  the  economic  relation  existing  between 
plants  and  animals.  The  lower  forms  of  plants  form  an  excellent 
introduction  to  the  lowest  animals,  and  the  conditions  existing  in 
a  balanced  aquarium  or  a  hay  infusion  serve  as  a  text  to  show  the 
larger  relations  existing  between  plants  and  animals.  In  the  study 
of  animal  life,  a  number  of  types  have  been  introduced,  not  with 
the  idea  that  the  pupil  will  take  all,  but  that  an  option  will  be  given. 
The  best  order  of  topics  in  the  spring  term  will  be  :  Protozoa;  the 
Metazoa  (either  sponge  or  hydra),  used  to  develop  the  concept  of  a 
collection  of  cells,  and  the  physiological  division  of  labor,  worms  or 
crustaceans,  the  latter  to  illustrate  adaptations  in  animals;  the 
insects  for  the  sake  of  elementary  classification  and  some  general 
biological  considerations  well  taken  up  there;  and  then  the  verte- 
brates. The  fish  may  be  used  as  a  study  of  adaptations  (in  which 
case  the  crustaceans  may  be  omitted),  and  the  frog,  when  taken  at 
the  spawning  season,  may  be  studied  for  its  development,  and  as  a 


8      PLAN  AND  PURPOSE  OF  THIS  BOOK 

basis  for  the  anatomical  basis  needed  in  the  study  of  human  physi- 
ology. Birds,  reptiles,  and  the  Mammalia  are  discussed  from  the 
economic  standpoint,  no  laboratory  work  being  required.  Field 
work  on  these  forms  should  be  encouraged.  The  later  chapters 
treat  of  man  as  an  animal  and  a  mammal.  After  a  brief  anatomical 
consideration  of  adaptations  in  the  skeleton  and  muscles,  the  skin 
as  an  organ  of  protection  and  excretion,  and  of  the  functions  of 
the  nervous  system,  a  study  of  foods  and  dietaries  is  begun.  Then 
come  digestion  and  absorption,  blood  and  its  circulation,  respiration 
and  excretion.  A  final  chapter  treats  of  health  and  disease  from  the 
standpoint  of  private  and  public  hygiene. 

If  the  work  begins  with  the  spring  term,  the  introductory  chap- 
ters may  be  taken,  then  the  seed  and  seedling,  root,  stem,  leaf, 
flower,  and  fruit,  reserving  the  treatment  of  the  cell,  simple  plants, 
and  the  bacteria  until  the  end  of  the  term.  This  allows  taking  up 
the  thread  in  the  fall  where  it  was  dropped,  with  an  introduction 
through  the  balanced  aquarium  and  the  hay  infusion  to  the  rela- 
tions existing  between  plants  and  animals.  The  best  order  of  topics 
in  the  fall  seems  to  be  :  protozoa,  some  simple  metazoan,  insects 
(taken  while  living  insects  may  still  be  obtained),  then  such  other 
groups  of  invertebrates  as  desired,  the  year's  work  again  culmi- 
nating with  the  vertebrates  and  biology  as  applied  to  the  himian 
animal. 

The  courses  as  outlined  above  are  held  together  and  made  con- 
tinuous by  certain  biological  ideas  and  ideals,  which  are  kept  before 
the  pupil  from  the  beginning  to  the  end  of  the  course.  Man  is  the 
center  of  the  course,  and  at  the  last  the  illustrations  are  applied  to 
the  human  mechanism. 

This  plan  includes  the  solving  of  a  number  of  problems  in  biology, 
each  of  which  is  more  or  less  determined  by  the  one  immediately 
preceding  it.  So  far  as  possible,  the  problems  have  a  himian 
interest.  Abstractions  are  not  part  of  the  thought  of  a  first-year 
pupil.  Concrete  problems,  related  when  possible  to  the  daily  life 
of  the  pupil,  have  been  used.  The  problems  are  stated  in  the  form 
of  laboratory  exercises  or  suggestions,  the  material  for  which  is  in 
the  hands  of  the  pupil  or  is  worked  out  as  a  demonstration  before 
the  class.  In  all  cases  the  laboratory  types  or  physiological  experi- 
ments demonstrate  some  important  principle  of  biology. 


PLAN  AND  PURPOSE  OF  THIS  BOOK  9 

The  laboratory  exercise  immediately  precedes  the  textbook 
discussion,  the  latter  being  used  to  clear  up  any  false  inferences 
the  pupil  may  have  made  from  the  specimen  in  hand  and  to  fix 
the  object  of  the  problem  in  the  mind  of  the  pupil.  Too  often 
has  a  laboratory  exercise  meant  nothing  to  a  pupil  but  "  busy 
work."  A  plainly  outlined  and  organized  plan  of  attack,  a  few 
references  to  the  text  or  to  previous  work  performed,  and  a  definite 
problem  will  result  in  better  and  more  definite  laboratory  work. 
For  use  with  this  book  a  manual  for  the  solution  of  laboratory 
problems  has  been  prepared  by  my  coworker,  Mr.  R.  W.  Sharpe. 
The  problems  to  be  solved  with  the  aid  of  the  manual  are  in 
boldface  italics.  It  is  neither  expected  or  desirable  that  a  pupil 
take  all  of  the  problems  so  indicated  in  a  year's  course. 

Two  styles  of  type  have  been  used  in  the  text.  The  larger 
type  contains  material  which  is  believed  to  be  of  first  impor- 
tance, the  smaller  type  the  less  important  topics.  The  manuscript 
was  read  in  its  entirety  by  Professor  H.  E.  Walter  of  Brown 
University.  To  him  I  owe  sincere  thanks  for  many  helpful 
criticisms  and  suggestions. 

Acknowledgments  are  due  to  Miss  A.  P.  Hazen,  Head  of  the 
Department  of  Biology  in  the  Eastern  District  High  School; 
to  H.  G.  Barber,  E.  A.  Bedford,  R.  E.  Call,  John  E.  McCarthy, 
C.  F.  Morse,  and  R.W. Sharpe  of  the  DeWitt  Clinton  High  School; 
Mr.  C.  W.  Beebe,  Curator  of  Birds,  New  York  Zoological  Park; 
W.  P.  Hay,  Head  of  the  Department  of  Biology  and  Chemistry 
of  the  Washington,  D.C.,  High  Schools;  and  Professor  A.  E.  Hill 
of  New  York  University,  for  their  careful  reading  and  criticism 
of  parts  or  all  of  the  proof. 

Thanks  are  due,  also,  to  Professor  E.  B.  Wilson,  Professor  G.  N. 
Calkins,  Mr.  William  C.  Barbour,  Dr.  John  A.  Sampson,  W.  C. 
Stevens,  and  C.  W.  Beebe,  Dr.  Alvin  Davison,  and  Dr.  Frank  Over- 
ton; to  the  United  States  Department  of  Agriculture;  the  New 
York  Aquarium;  the  Charity  Organization  Society;  the  Folmer 
and  Schwing  Company,  Rochester,  N.Y.  ;  and  the  American 
Museum  of  Natural  History,  for  permission  to  copy  and  use  certain 
photographs  and  cuts  which  have  been  found  useful  in  teaching. 
My  acknowledgments  are  also  due  to  Mr.  A.  C.  Doane  of  the 
Central  High  School,  Grand  Rapids,  Mich.,  for  permission  to  use 


10  PLAN  AND  PURPOSE  OF  THIS  BOOK 

extracts  from  his  excellent  article  in  School  Science  on  the  effects 
of  Alcohol.  R.  W.  Coryell  and  J.  W.  Tietz,  two  of  my  former 
pupils,  made  several,  of  the  photographs  of  experiments. 

At  the  end  of  each  of  the  following  chapters  is  a  list  of  books  which  have 
proved  their  use  either  as  reference  reading  for  students  or  as  aids  to  the 
teacher.  Most  of  the  books  mentioned  are  within  the  means  of  the  small 
school.  Two  sets  are  expensive :  one,  The  Natural  History  of  Plants, 
by  Kerner,  translated  by  Oliver,  published  by  Henry  Holt  and  Company, 
in  two  volumes,  at  $11 ;  the  other.  Plant  Geography  upon  a  Physiological 
Basis,  by  Schimper,  pubhshed  by  the  Clarendon  Press,  $12;  but  both 
works  are  invaluable  for  reference. 

For  a  general  introduction  to  physiological  biology,  Parker,  Elementary 
Biology,  The  Macmillan  Company ;  Sedgwick  and  Wilson,  General 
Biology,  Henry  Holt  and  Company  ;  and  Verworn,  General  Physiology, 
The  Macmillan  Company,  are  most  useful  and  inspiring  books. 

Two  books  stand  out  from  the  pedagogical  standpoint  as  by  far  the  most 
helpful  of  their  kind  on  the  market.  No  teacher  of  botany  or  zoology  can 
afford  to  be  without  them.  They  are  :  Lloyd  and  Bigelow,  The  Teaching 
of  Biology,  Longmans,  Green,  and  Company,  and  C.  F.  Hodge,  Nature 
Study  and  Life,  Ginn  and  Company.  Other  books  of  value  from  the  teach- 
er's standpoint  are  :  Ganong,  The  Teaching  Botanist,  The  Macmillan  Com- 
pany ;  L.  H.  Bailey,  The  Nature  Study  Idea,  Doubleday,  Page,  and  Com- 
pany, and  McMurry's  How  to  Study,  Houghton,  Mifflin  Company. 


CONTENTS 

CHAPTKR  PAOK 

T.    SoMK  Reasons  for  the  Study  of  Biology   .        .        .VI 

IT.     The  Surroundings  or  Environment  of  Living  Things  17 

III.  The  Functions  and  Composition  of   Living  Things  26 

IV.  Flowers  and  their  Work        ....  34 
V.    Fruits  and  their  Uses 51 

VI.    Seeds  and  Seedlings 65 

VII.     Roots  and  their  Work 84 

VIII.     The  Structure  and  Work  of  the  Stem       ...  98 

IX.    Leaves  and  their  Work 115 

X.     Our    Forests;    their   Uses  and  the   Necessity   for 

THEIR  Protection 133 

XL    The  Various  Forms  of  Plants  and  how  they  Repro- 
duce Themselves 144 

XII.    How  Plants  are  modified  by  their  Surroundings  .  159 

XIII.  How  Plants  benefit  and  harm  Mankind     .        .        .  ^70 

XIV.  The  Relations  of  Plants  to  Animals          .        .        .  184 
XV.    The  Protozoa 190 

XVI.    The  Metazoa  —  Division  of  Labor        ....  199 
XVII.    The   Worms,   a   Study   of   Relations    to    Environ- 
ment         212 

XVIII.     The  Crayfish.    A  Study  of  Adaptations    .        .        .  221 

XIX.    The   Insects 233 

XX.    General  Considerations  from  the  Study  of  Insects  249 

XXL    The  Mollusks 267 

11 


12  CONTENTS 

CHAPTER  PAOS 

XXII.    The  Vertebrate  Animals        .        .        •        o        .        .  274 

Fishes 275 

Amphibia.     The  Frog 285 

Reptiles 293 

Birds      . 297 

Mammals 311 

XXITI.     Man,  A  Mammal 319 

XXIV.    Foods  and  Dietaries 330 

XXV.    Digestion  and  the   Absorption 352 

XXVI.     The  Blood  and  its  Circulation 366 

XXVII.    Respiration  and  Excretion 382 

XXVIII.     The  Nervous  System  and  Organs  of  Sense        .        .  399 

XXIX.     Health  and  Disease  —  A  Chapter  on  Civic  Biology  418 

Index 437 


I.  SOME  REASONS  FOR  THE  STUDY  OF  BIOLOGY 

What  is  Biology?  —  Biology  is  the  study  of  living  beings,  both 
plant  and  animal.  Inasmuch  as  man  is  an  animal,  the  study  of 
biology  includes  the  study  of  man  in  his  relations  to  the  plants 
and  the  animals  which  surround  him.  Most  important  of  all 
is  that  branch  of  biology  which  treats  of  the  mechanism  we  call 
the  human  body,  —  of  its  parts  and  their  uses,  and  its  repair. 
This  subject  we  call  human  physiology. 

Why  study  Biology? — Although  biology  is  a  very  modern  science, 
it  has  found  its  way  into  most  high  schools;  and  an  increasingly 
large  number  of  boys  and  girls  are  yearly  engaged  in  its  study. 
The  question  might  well  be  asked  by  any  of  these  students.  Why 
do  I  take  up  the  study  of  biology?  Of  what  practical  value  is  it 
to  me?  Aside  from  the  discipHne  it  gives  me,  is  there  anything 
that  I  can  take  away  which  will  help  me  in  my  future  life  as  a  boy 
or  girl  with  only  a  high  school  education? 

Human  Physiology.  —  The  answer  to  this  question  is  plain. 
If  the  study  of  biology  will  give  us  a  better  understanding  of  our 
own  bodies  and  their  care,  then  it  certainly  is  of  use  to  us.  That 
phase  of  biology  known  as  physiology  deals  with  the  uses  of  the 
parts  of  a  plant  or  animal ;  human  physiology  and  hygiene  deal  with 
the  uses  and  care  of  the  parts  of  the  human  animal.  The  preven- 
tion of  sickness  is  due  in  a  large  part  to  the  study  of  hygiene.  It 
is  estimated  that  400,000  out  of  the  1,600,000  deaths  that  occur 
yearly  in  this  country  could  l^e  averted  if  only  all  people  hved  in 
a  hygienic  manner.  In  its  application  to  the  lives  of  each  of  us, 
as  a  member  of  our  family,  as  a  member  of  the  school  we  attend, 
and  as  a  future  citizen,  a  knowledge  of  hygiene  is  of  the  greatest 
importance. 

Relations  of  Plants  to  Animals.  —  But  there  are  other  reasons 
why  an  educated  person  should  know  something  about  biology. 
We  do  not  always  realize  that  if  it  were  not  for  the  green  plants, 
there  would  be  no  animals  on  the  earth.    Green  plants  furnish 

13 


14     SOME  REASONS  FOR  THE  STUDY  OF  BIOLOGY 

animals  with  their  food.  Even  the  meat-eating  animals  feed  in 
the  long  run  upon  those  that  feed  upon  plants.  How  the  plants 
manufacture  this  food  and  the  relation  they  have  to  animals  will 
be  discussed  in  later  chapters.  Plants  furnish  man  with  the 
greater  part  of  his  food  in  the  form  of  grains  and  cereals,  fruits 
and  nuts,  edible  roots  and  leaves ;  they  provide  his  domesticated 
animals  with  food ;  they  give  him  timber  for  his  houses  and  wood 
and  coal  for  his  fires ;  they  provide  him  with  pulp  wood,  from 
which  he  makes  his  paper,  and  oak  galls,  from  which  he  obtains 
ink.  Much  of  man's  clothing  and  the  thread  with  which  they 
are  sewed  together  come  from  fiber-producing  plants.  Most  medi- 
cines, beverages,  flavoring  extracts,  and  spices  are  plant  products, 
while  plants  are  made  use  of  in  hundreds  of  ways  in  the  useful 
arts  and  trades,  producing  varnishes,  dyestuffs,  rubber,  and  other 
useful  products. 

Bacteria  in  their  Relation  to  Man.  —  In  still  another  way,  cer- 
tain plants  vitally  affect  mankind.  These  tiny  plants,  so  small 
that  millions  can  exist  in  a  single  drop  of  fluid,  are  called  bacteria 
or  germs.  Existing  almost  everjrwhere  about  us,  —  in  water,  soil, 
food,  and  the  air,  —  they  play  a  tremendous  part  in  shaping  the 
destiny  of  man  on  the  earth.  They  help  him  in  that  they  act  as 
scavengers,  causing  things  to  decay;  they  help  make  cheese  and 
butter;  they  assist  the  tanner;  and  the  farmer  could  not  do  with- 
out them;  but  they  likewise  spoil  our  meat  and  fish,  and  our 
vegetables  and  fruits;  they  sour  our  milk,  and  make  our  canned 
goods  spoil.  More  than  this,  they  cause  diseases,  among  others 
tuberculosis,  a  disease  so  harmful  as  to  be  called  the  *'  white 
plague. ''  Fully  one  half  of  all  yearly  deaths  are  caused  by  these 
plants.  So  important  are  the  bacteria  that  a  subdivision  of  biol- 
ogy, called  bacteriology,  has  been  named  after  them,  and  hundreds 
of  scientists  are  devoting  their  lives  to  the  study  of  germs  and 
their  control.  The  greatest  of  all  bacteriologists,  Louis  Pasteur, 
once  said,  *'It  is  within  the  power  of  man  to  cause  all  parasitic 
diseases  (diseases  mostly  caused  by  bacteria)  to  disappear  from 
the  world."  His  prophecy  is  gradually  being  fulfilled,  and  it  may 
be  the  lot  of  some  boys  or  girls  who  read  this  book  to  do  their 
share  in  helping  to  bring  this  condition  of  affairs  about. 

The  Relation  of  Animals  to  Man.  —  Animals  also  play  an  im- 


SOME  REASONS  FOR  THE  STUDY  OF  BIOLOGY    15 

portant  part  in  the  world  in  causing  and  carrying  disease.  Ani- 
mals that  cause  disease  are  usually  tiny,  and  live  upon  other 
animals  as  parasites ;  that  is,  they  get  their  living  from  their  hosts 
on  which  they  feed.  Among  the  diseases  caused  by  parasitic 
animals  are  malaria,  yellow  fever,  the  sleeping  sickness,  and  hook- 
worm disease.  Animals  also  carry  disease,  especially  the  flies  and 
mosquitoes;  rats  and  other  animals  are  also  well  known  as 
spreaders  of  disease. 

From  a  money  standpoint,  animals  called  insects  do  much  harm. 
It  is  estimated  that  in  this  country  alone  they  are  annually  re- 
sponsible for  $800,000,000  worth  of  damage. 

The  Uses  of  Animals  to  Man.  —  We  all  know  the  uses  man 
has  made  of  the  domesticated  animals  for  food  and  as  beasts  of 
burden.  But  many  other  uses  are  found  for  animal  products, 
and  materials  made  from  animals.  Wool,  furs,  leather,  hides, 
feathers,  and  silk  are  examples.  The  arts  make  use  of  ivory, 
tortoise  shell,  corals,  and  mother  of  pearl;  from  animals  come 
perfumes  and  oils,  glue,  lard,  and  butter;  animals  produce  honey, 
wax,  milk,  eggs,  and  various  other  commodities. 

The  Conservation  of  our  Natural  Resources.  —  Still  another 
reason  why  we  should  study  biology  is  that  we  may  work  under- 
standingly  for  the  conservation  of  our  natural  resources,  especially 
our  forests.  The  forest,  aside  from  its  beauty  and  its  health- 
giving  properties,  holds  water  in  the  earth.  It  keeps  the  water 
from  drying  out  of  the  earth  on  hot  days  and  from  running  off  on 
rainy  days.  Thus  a  more  even  supply  of  water  is  given  to  our 
rivers,  and  thus  freshets  are  prevented.  Countries  that  have  been 
deforested,  such  as  China,  Italy,  and  parts  of  France,  are  now  sub- 
ject to  floods,  and  are  in  many  places  barren.  On  the  forests 
depend  our  timber,  our  future  water  power,  and  the  future  com- 
mercial importance  of  cities  which,  like  New  York,  are  located 
at  the  mouths  of  our  navigable  rivers. 

Plants  and  Animals  mutually  Helpful.  —  The  study  of  biology 
also  shows  us  the  interrelation  existing  between  plants  and  animals 
on  the  earth.  Most  plants  and  animals  stand  in  an  attitude  of 
mutual  helpfulness  to  one  another,  plants  providing  food  and 
shelter  for  animals;  animals  giving  off  waste  materials  useful 
to  plants  in  the  making  of  food.     We  also  learn  that  plants  and 


16    SOME  REASONS  FOR  THE  STUDY  OF  BIOLOGY 

animals  need  the  same  conditions  in  their  surroundings  in  order  to 
live :  water,  air,  food,  a  favorable  temperature,  and  usually  light. 
We  learn  that  the  life  processes  of  both  plants  and  animals  are 
essentially  the  same,  and  that  the  living  matter  of  a  tree  is  as 
much  alive  as  is  the  living  matter  in  a  fish,  a  dog,  or  a  man. 

Biology  in  its  Relation  to  Society.  —  Finally,  the  study  of  biology 
should  be  part  of  the  education  of  every  boy  and  girl,  because  society 
itself  is  founded  upon  the  principles  which  biology  teaches.  Plants 
and  animals  are  living  things,  each  taking  what  it  can  from  its  sur- 
roundings; they  enter  into  competition  with  one  another,  and 
those  which  are  the  best  fitted  for  life  outstrip  the  others.  Health 
and  strength  of  body  and  mind  are  factors  which  tell  in 
winning.  The  strong  may  hand  down  to  their  offspring  the  char- 
acteristics which  make  them  the  winners. 

Man  has  made  use  of  this  message  of  nature,  and  has  developed 
improved  breeds  of  horses,  cattle,  and  other  domestic  animals. 
Plant  breeders  have  likewise  selected  the  plants  or  seeds  that  have 
varied  toward  better  plants  and  thus  have  stocked  the  earth  with 
hardier  and  more  fruitful  domesticated  plants.  Man's  dominion 
over  the  living  things  of  the  earth  is  tremendous.  It  is  due  to  the 
understanding  of  the  principles  which  underlie  the  science  of  biology. 


II.  THE  SURROUNDINGS  OR  ENVIRONMENT  OF  LIVING 

THINGS 

Environment.  —  A  plant  or  an  animal  living  on  the  earth  may  be 
said  to  come  in  contact  with  air,  water,  and  soil.  It  may  be  influ- 
enced by  hght,  varying  conditions  of  temperature,  of  the  atmosphere 
or  water,  the  presence  or  absence  of  food  materials,  and  some  other 
things.  We  shall  later  see  that  the  sum  total  of  these  various  fac- 
tors, acting  upon  the  living  thing,  may  cause  great  changes  to  take 
place  in  the  structure  or  habits  of  a  plant  or  animal.  The  surround- 
ing forces  which  act  upon  living  things  form  their  environment. 

In  order  better  to  understand  what  a  living  plant  or  animal 
takes  from  its  environment,  we  must  find  out  something  about  the 
air,  water,  and  the  soil,  for  it  is  with  these  factors  that  the  plant 
and  the  animal  are  in  immediate  contact. 

Prohlem  I.  A  study  of  the  common  elem^eiits  in  the  en- 
vironm'ent  of  living  things.    {.Laboratory  Manual y  Prob.  7.)^ 

(a)  Xitrogen. 

(b)  Oxygen  and  oxidation. 

(c)  Hydrogen. 

(d)  Carbon  and  Carbon  dioxide. 


The  Composition  of  the  Air.  —  If  we 

invert  a  large  bell  jar  over  a  deep 
tray  containing  water,  having  pre- 
viously placed  a  float  hokling  a  bit  of 
burning  phosphorus  upon  the  surface 
of  the  water,  we  find  that  as  the  phos- 
phorus burns,  the  water  slowly  rises  in 
the  jar.     After  a  Httle  the  phosphorus 

goes   out.      The  water  now  displaces  a      Experiment  to  show  the  amount 
VOllune  equal  to   about  one  fifth  of  the        of  nitrogen  present  in  the  air. 

1  Sharpe.  A  Laboratory  Manual  Jar  the  Solution  oj  Problems  in  Biology,  American 
Book  Company. 


HUNT.  ES.  BIO.  —  2 


17 


18  ENVIRONMENT  OF  LIVING  THINGS 

space  occupied  by  the  air  in  the  jar.  When  the  water  reaches 
this  height,  it  goes  no  higher,  and,  no  matter  how  many  times 
the  experiment  is  repeated,  the  phosphorus  invariably  goes  out 
when  the  water  displaces  one  fifth  of  the  air  in  the  jar. 

Evidently,  the  burning  of  the  phosphorus  uses  up  some  gas  within 
the  jar,  which  supports  the  flame,  and  the  gas  which  remains  in  the 
jar,  occupying  about  four  fifths  of  the  space,  does  not  have  the  power 
of  maintaining  the  flame.  The  former  gas  is  called  oxygen;  the 
latter,  nitrogen.  These  two  gases  form  the  principal  constituents 
of  the  air  in  the  proportion  seen  in  the  experiment. 

Chemical  Elements.  —  All  the  materials  of  this  universe,  both  Uv- 
ing  and  lifeless,  are  classified  by  chemists  as  either  chemical  elements 
or  chemical  compounds.  A  chemical  element  is  a  substance  which 
has  never  been  decomposed  into  anything  simpler  in  composition. 
Examples  of  such  elements  are  oxygen,  making  up  about  one  fifth 
of  the  atmosphere;  nitrogen,  composing  nearly  all  the  remainder  of 
pure  air;  carbon,  an  element  that  enters  into  the  composition  of  all 
organic  matter;  and  over  seventy  others  of  more  or  less  importance 
to  us  in  the  study  of  biology. 

Nitrogen.  —  The  physical  properties  (those  which  we  determine 
through  our  senses)  of  nitrogen  are  its  lack  of  color,  taste,  and  odor. 
Its  chief  chemical  characteristics  are  its  inability  to  support  com- 
bustion and  its  shght  tendency  to  combine  with  other  substances. 
We  shall  later  find  that  nitrogen  is  one  of  the  most  important  chem- 
ical elements  found  in  Uving  matter.  In  spite  of  this,  animals  and 
most  plants  are  absolutely  unable  to  take  any  nitrogen  from  the 
air,  no  matter  how  much  they  may  need  it. 

The  other  element  in  the  air,  oxygen,  is  taken  out  by  the  plants 
and  animals.  We  shall  be  able  to  see  how,  after  studying  the  prop- 
erties of  oxygen. 

Preparation  of  Oxygen.  Elements  and  Compounds.  —  Oxygen 
may  be  prepared  by  heating  half  a  teaspoonful  of  chlorate  of 
potash  with  a  little  less  than  its  bulk  of  black  oxide  of  man- 
ganese in  a  test  tube  over  a  Bunsen  flame  or  a  spirit  lamp. 
After  a  moment  a  glowing  match  inserted  in  the  mouth  of  a  test 
tube  bursts  into  a  bright  flame.  Evidently  the  match  burns  more 
brightly  because  of  the  presence  of  a  gas  which  has  been  loosed 
from  the  materials  in  the  test  tube.     These  materials  are  chemical 


ENVIRONMENT  OF   LIVING   THINGS 


19 


compounds  ;  that  is,  chemical  elements  which  are  united  by  certain 
chemical  laws  to  form  substances  called  compounds.  Compounds 
are  quite  different  in  their 
properties  from  the  elements 
which  compose  them.  Such 
is  the  chlorate  of  potash,  which 
contains  the  elements  oxygen, 
chlorine,  and  potassium.  Heat- 
ing this  with  oxide  of  manga- 
nese causes  the  oxygen  to  be 
released  in  the  form  of  a  gas. 
This  is  an  example  of  a  chem- 
ical change. 

Properties  of  Oxygen.  — Oxy- 
gen, when  carefully  prepared, 
is  found  to  be  colorless,  odor- 
less, and  tasteless.  It  mak(\s 
up  about  one  fifth  of  the  air. 
Combined  with  other  sub- 
stances, it  forms  a  very  large 
part  by  weight  of  water,  rocks, 
minerals,  and  the  bodies  of  plants  and  animals.  Oxygen  has 
the  very  important  property  of  uniting  with  many'  other  sub- 
stances. 

The  chemical  union  of  oxygen  with  any  other  substance  is  called 
oxidation.  Oxidation  of  some  sort  may  take  place  wherever  oxy- 
gen is  present.  This  fact  has  a  far-reaching  significance  in  the 
understanding  of  the  most  important  problems  of  biology. 

Oxidation  in  a  Match.  — .The  simple  process  of  striking  a  sulphur  match 
gives  us  another  illustration  of  this  process  of  oxidation.  The  head  of  the 
match  is  formed  of  a  combination  of  phosphorus,  sulphur,  and  some  other 
materials.  Phosphorus  is  a  chemical  element  distingfuished  by  its  extreme 
inflammability  ;  that  is,  it  unites  with  oxygen  at  a  comparatively  low  tem- 
perature, producing  a  flame.  Sulphur  is  another  chemical  element  that 
combines  somewhat  easily  with  oxygen  but  at  a  much  higher  temperature. 
The  rest  of  the  match  head  is  made  up  of  red  lead,  niter,  or  some  other  sub- 
stance that  will  release  oxygen,  and  some  glue  or  gum  to  bind  the  materials 
together.  The  heat  caused  by  the  friction  of  the  match  head  against  the 
striking  surface  is  enough  to  cause  the  phosphorus  to  ignite ;  this  in  turn 


ricparutioii  ol  Oxygeu. 


20 


ENVIRONMENT  OF  LIVING   THINGS 


ignites  the  sulphur,  and  finally  the  wood  of  the  match,  composed  largely 
of  the  element  carbon,  is  lighted  and  oxidized.  If  we  could  take  out  the 
different  chemical  elements  of  which  the  match  is  formed  and  oxidize  them 
separately,  we  should  find  that  the  amount  of  heat  needed  to  start  the  oxi- 
dation of  the  substances  would  vary  greatly.  The  element  phosphorus,  for 
example,  is  kept  under  water  in  a  glass  jar  be- 
cause of  the  extreme  readiness  with  which  it  ig- 
nites in  the  presence  of  oxygen.^ 

Slow  Oxidation.  —  Oxidation  may  take 
place  slowly,  as  may  be  seen  in  the  rusting 
of  an  iron  nail.  Rust  is  iron  oxide,  and  is 
formed  by  the  union  of  iron  and  oxygen. 
This  kind  of  oxidation  is  said  to  be  a  slow 
oxidation.  Slow  oxidations  are  constantly 
taking  place  in  nature  and  are  a  part  of  the 
process  of  decay  and  of  breaking  down  of 
complex  materials  into  simpler  materials. 

Heat  given  off  as  Result  of  Oxidation.  — 
One  of  the  most  important  effects  of  oxida- 
tion lies  in  the  fact  that,  when  anything 
is  oxidized,  heat  is  produced.  This  heat 
may  be  of  the  greatest  use.  Coal,  when 
oxidized,  gives  off  heat ;  this  heat  boils  the 
water  in  the  tubes  of  a  boiler;  steam  is 
generated,  wheels  of  an  engine  turn,  and 
work  is  performed.  The  energy  released 
l)y  the  burning  of  coal  may  be  transformed 
into  any  kind  of  work  power.  Energy  is 
the  ability  to  perform  work.  We  shall  later 
find  that  the  oxidation  of  certain  materials 
in  the  bodies  of  plants  or  animals  releases 
energy.  The  heat  of  the  human  body  is 
maintained  by  constant  oxidation  of  food 
materials  within  the  body. 
The  Composition  of  Water.  —  If  an  electric  current  is  passed 
through  water  ^  by  means  of  the  apparatus  shown  in  the  Figure,  it 

1  The  teacher  may  later  introduce  experiments  in  chemistry  to  demonstrate  the 
physical  appearance  of  such  other  elements  as  are  ussd  by  plants  in  food  making. 

2  A  little  sulphuric  acid  must  be  added  to  make  the  liquid  a  better  conductor. 


Apparatus  for  separating 
water  into  the  two  ele- 
ments hydrogen  and 
oxygen. 


ENVIRONMENT  OF   LIVING   THINGS  21 

is  found  that  the  water  separates  into  two  gases,  one  of  which 
occupies  twice  as  much  space  as  the  other  in  the  tubes.  If  we 
test  the  gas  present  in  smaller  quantity,  we  find  it  to  be  oxygen. 
The  other  gas,  colorless,  tasteless,  and  odorless  like  the  oxygen, 
differs  from  it  by  igniting  with  a  slight  explosion  if  a  burning  match 
or  splinter  is  introduced  in  it.  As  it  burns,  drops  of  water  are 
formed,  showing  that  it  is  passing  back  to  its  original  condition, 
that  is,  it  is  uniting  with  oxygen  to  form  water.  This  gas  is  hydro- 
gen. Hydrogen  has  a  great  chemical  affinity  or  Uking  for  other 
elements,  hence  it  is  usually  found  in  nature  combined  with  other 
elements,  as  with  oxygen  to  form  water. 

The  Composition  of  the  Soil.  —  The  covering  of  the  earth  was 
probably  very  different  in  former  ages  from  what  it  now  is.  Its 
molten  plastic  mass  after  cooling  formed  rock.  This  rock,  by  the 
work  of  the  wind,  frost,  heat,  and  water,  and  plants,  has  in  part 
been  broken  into  small  bits.  This  is  inorganic  soil,  such  as  sea 
sand  and  gravel.  Such  soil  is  formed  usually  of  several  elements 
found  in  rocks,  such  as  calcium,  sodium,  magnesium,  silicon, 
potassium,  and  iron  combined  with  oxygen. 

A  visit  to  the  woods  or  to  a  well-kept  garden  shows  us  that  there 
is  another  kind  of  soil  than  the  inorganic  soil  just  mentioned.  This 
is  the  rich,  dark  soil  containing  humus.  Humus  is  made  up  in  part 
of  dead  organic  matter,  the  decayed  remains  of  plants  and  ani- 
mals. In  such  soil  we  should  find  relatively  more  water  than  in 
inorganic  soil.  If  we  could  test  the  chemical  elements  to  be  found 
in  humus,  we  should  find  nitrogen,  hydrogen,  oxygen,  and  also 
carbon,  an  important  element  found  in  all  organic  matter. 

Carbon.  —  Carbon  is  found  in  many  conditions  in  nature.  It 
makes  up  a  large  part  of  the  bodies  of  plants  and  animals,  and  of 
coal,  and  it  exists  in  a  nearly  pure  state  in  the  diamond.  The 
presence  of  carbon  can  usually  be  detected  by  partially  burning 
the  substance,  carbon  showing  as  a  black  substance  without  taste 
or  odor.  Carbon  may  be  collected  by  allowing  a  candle  flame  to 
burn  in  contact  with  the  underside  of  a  sheet  of  glass.  The 
black  deposit  is  almost  pure  carbon. 

Oxidation  of  Carbon  and  its  Result.  —  If  we  burn  a  candle  in 
a  closed  jar  containing  air,  the  flame  soon  begins  to  flicker,  and  then 
goes  out.      If  the  cover  of  the  jar  is  carefully  removed,  and  a 


22  ENVIRONMENT  OF  LIVING  THINGS 

burning  match  lowered  into  the  jar,  the  match  will  at  once  go  out, 
showing  the  presence  of  a  gas  heavier  than  air  which  will  not 
support  a  flame.  We  might  suspect  the  presence  of  nitrogen,  but 
nitrogen  would  not  respond  to  the  test  which  follows.  If  we  pour 
into  the  jar  a  few  spoonfuls  of  limewater/  a  colorless  liquid,  and 
shake  it  up  with  the  gas  in  the  jar,  the  limewater  turns  milky  in 
color.  This  is  a  test  for  a  compound  known  as  carbon  dioxide. 
This  compound  was  evidently  formed  by  the  union  of  the 
carbon  with  the  oxygen  of  the  air  in  the  jar. 

All  organic  or  living  substances,  when  oxidized,  form 
carbon  dioxide.  That  oxidation  of  carbon  takes  place 
within  our  own  bodies  may  easily 
be  proved  by  exhaling  through  a 
clean  glass  tube  into  some  lime- 
water.  The  heat  of  our  body 
(98.5°  F.)  is  the  result  of  oxidation     ^ 

taking    place    within    the    body.      ^      j  jti —  h  ^ 

The  heat  given  off  from  oxidation     "t:  ;;        ;      '.  TT 

.  .  Diagram   of   combustion   or   rapid 

of  wood   or   coal   m   a  stove   is   de-  oxidation  in  a  stove. 

termined  by  the  supply  of  oxygen 

we  allow  to  pass  to  the  burning  material.  If  we  open  the 
draft,  allowing  more  oxygen  to  get  to  the  fire,  we  increase 
the  heat  by  more  rapid  oxidation ;  if  we  shut  off  the  oxygen 
supply,  we  decrease  the  amount  of  oxidation.  Does  this  help  to 
explain  our  deep  breathing  after  doing  hard  physical  exercise? 

Problem  II,    Are  mineral  matter  and  water  present  in  liv- 
ing things?    {Laboratory  Manual,  Prob.  II.) 
(a)  Mineral  matter. 
ib)   Water. 

Mineral  Matter  in  Living  Things.  —  If  a  piece  of  wood  is  burned  in  a 
very  hot  fire,  the  carbon  in  it  will  aU  be  consumed,  and  eventually  nothing 
will  be  left  except  a  grayish  ash.  This  ash  is  well  seen  after  a  wood  fire  in 
the  fireplace,  or  after  a  bonfire  of  dry  leaves.  It  consists  entirely  of  min- 
eral matter  which  the  plant  has  taken  up  from  the  soil  dissolved  in  water, 
and  which  has  been  stored  in  the  wood  or  leaves. 

1  Limewater  can  be  made  by  shaking  up  a  piece  of  quicklime  the  size  of  your 
fist  in  about  two  quarts  of  water.  Filter  or  strain  the  limewater  into  bottles,  and  it 
is  ready  for  use. 


ENVIRONMENT  OF   LIVING   THINGS  23 

If  we  were  able  by  careful  analysis  to  reduce  a  plant  and  an  animal 
to  the  chemical  compounds  of  which  they  were  formed,  we  should  discover 
that  both  contained  mineral  material.  We  have  just  seen  examples  of 
this  in  plants.  Mineral  matter  is  found  in  bone,  in  the  shells  covering 
mollusks  (clams,  snails,  etc.),  and  in  other  parts  of  the  bodies  of  animals. 

Water  in  Living  Things.  —  Water  forms  an  important  part  of  the  sub- 
stance of  plants  and  animals.  This  can  easily  be  proved  by  weighing  a 
number  of  green  leaves,  placing  them  in  a  hot  oven  for  a  few  moments,  and 
then  re  weighing.  The  same  experiment  made  with  a  soft-bodied  animal, 
as  the  oyster,  would  show  even  more  water  than  in  leaves.  Some  jelly- 
fish are  composed  of  over  90  per  cent  water.  The  human  body  contains 
about  65  per  cent  water. 

Gases  Present.  —  Some  gases  are  found  in  a  free  state  in  the  bodies  of 
plants  or  animals.  Oxygen  is  of  course  present  wherever  oxidation  is 
taking  place,  as  is  carbon  dioxide.  Other  gases  may  be  present  in  minute 
quantities. 

Problem  JII,  The  foods  that  living  organisms  need.  {Lab- 
oratory Manual,  Prob.  III.) 

Composition  of  Living  Matter.  —  The  living  part  of  a  plant  or 
animal  is  made  up  of  the  elements  carbon,  hydrogen,  oxygen,  and 
nitrogen,  with  a  very  minute  amount  of  several  other  elements, 
which  collectively  we  may  call  mineral  matter.  The  living  part 
of  a  plant  corresponds  closely  in  chemical  composition  to  the  living 
part  of  an  animal.  The  sugar  found  in  grains  or  roots  of  plants 
has  nearly  the  same  chemical  formula  as  the  animal  sugar  found 
in  the  liver  of  man ;  the  oils  of  a  nut  or  fruit  are  of  composition 
closely  allied  to  the  fat  in  the  body  of  an  animal.  These  build- 
ing materials  of  a  plant  or  animal  may  be  placed  in  one  of  the 
three  following  groups  of  substances :  carbohydrates,  materials 
containing  a  certain  proportion  of  carbon,  hydrogen,  and  oxygen ; 
fats  and  oils,  which  contain  chiefly  hydrogen  and  carbon  with  less 
oxygen;  and  nitrogenous  or  proteid  substances,  which  contain 
nitrogen  in  addition  to  the  above-mentioned  elements.  The  above 
three  kinds  of  organic  materials  also  form  a  large  part  of  the  foods 
of  all  animals  and  plants. 

Foods.  —  What  is  a  food?  We  know  that  if  we  eat  a  certain 
amount  of  proper  foods  at  regular  times,  we  shall  be  able  to  go  on 
doing  a  certain  amount  of  work,  both  manual  and  mental.  We 
know,  too,  that  day  by  day,  if  our  general  health  is  good,  we  may 


24  ENVIRONMENT  OF  LIVING   THINGS 

be  adding  weight  to  our  body,  and  that  added  weight  comes  as  the 
result  of  taking  food  into  the  body.  What  is  true  of  a  boy  or  girl 
is  equally  true  of  plants.  If  food  is  supplied  in  proper  quantity 
and  proportion,  they  will  live  and  grow ;  if  the  food  supply  is  cut 
off,  or  even  greatly  reduced,  they  will  suffer  and  may  die.  From 
this,  the  definition  which  follows  is  evident.  A  food  is  a  substance 
that  forms  the  material  for  the  growth  or  repair  of  the  body  of  a  plant 
or  animal  or  that  furnishes  energy  for  it. 

Nutrients.  —  Organic  food  substances  may  be  classed  into  a 
number  of  groups,  each  of  which  may  be  detected  by  means  of  its 
chemical  composition.  Such  groups  of  food  substances  are  known 
as  nutrients.     Let  us  now  examine  the  nutrients.^ 

Carbohydrates.  —  Starch  and  sugar  are  common  examples  of 
this- group  of  substances.  The  former  we  find  in  our  cereals,  bread, 
cake,  and  most  of  our  vegetables.  Several  forms  of  sugar  are 
commonly  used  as  food ;  for  example,  cane  sugar,  beet  sugar,  and 
glucose  or  grape  sugar.  Glucose,  found  as  the  natural  sugar  of 
grapes,  honey,  and  fruits,  is  manufactured  commercially  by  pour- 
ing sulphuric  acid  over  starch.  It  is  used  as  an  adulterant  for 
many  kinds  of  foods,  especially  in  sirups,  honey,  and  candy. 

Fats  and  Oils.  —  Fats  and  oils  form  an  important  part  of  the 
composition  of  plants  and  animals.  Examples  of  food  in  the 
form  of  fat  are  butter  and  cream,  the  oils  in  nuts,  olives,  and 
other  fruits,  and  fat  in  animals. 

Proteids.  —  Nitrogenous  foods,  or  proteids,  contain  the  element 
nitrogen  in  addition  to  carbon,  hydrogen,  and  oxygen  of  the  car- 
bohydrates and  fats  and  oils.  They  include  some  of  the  most 
complex  substances  known  to  the  chemist,  and,  as  we  shall  see,  have 
a  chemical  composition  very  near  to  that  of  living  matter.  Pro- 
teids occur  in  several  different  forms.  White  of  egg,  lean  meat, 
beans,  and  peas  are  examples  of  substances  composed  in  a  large 
part  of  proteids. 

Inorganic  Foods.  —  Water  and  various  salts,  some  of  which, 
as  lime,  may  be  found  in  drinking  water,  form  important  parts  in 
the  diet  of  plants  and  animals.  Later  we  shall  see  that  green 
plants,  although  they  use  precisely  the  same  foods  as  we  do,  take 
into  their  bodies  the  chemical  elements  which  form  foods.  From 
1  For  a  fuller  explanation  of  nutrients,  see  Chapters  VI  and  XXIV. 


ENVIRONMENT   OF   LIVING   THINGS  25 

these  raw  food  materials,  organic  foods  are  manufactured  in  the 
body  of  the  plant. 

Books  for  Reference 
elementary 

Sharpe,  A  Laboratory  Manual  for  the  Solution  of  Problems  in  Biology.     American 

Book  Company. 
Avery-Sinnott,  First  Lessons  in  Physical  Science.     American  Book  Company. 
Eddy,  Experimental  Physiology  and  Anatomy.       American  Book  Company. 
Snyder,  The  Chemistry  of  Plant  and  Animal  Life.     The  Macmillan  Company. 

ADVANCED 

Coulter,  Barnes,  and  Cowles,  A  Textbook  of  Botany,  Part  II.    American  Book  Com- 
pany. 
Foster,  A  Textbook  of  Physiology.     The  Macmillan  Company. 
Green,  Vegetable  Physiology.     J.  and  A.  Churchill. 
Sedgwick  and  Wilson,  General  Biology.     Henry  Holt  and  Company. 


III.  THE  FUNCTIONS  AND  COMPOSITION  OF  LIVING 

THINGS 

Problein  IV,    An  introduction  to  the  nature  and  worh  of 
living  organisms.    (Laboratory  Manual,  Prob.  IV.) 
ia)  A  living  plant, 
ib)    A  living  insect. 

A  Living  Plant  and  a  Living  Animal  Compared. — A  walk  into  the 
fields  or  any  vacant  lot  on  a  day  in  the  early  fall  will  give  us  first- 
hand acquaintance  with  many  common  plants  which,  because  of 
their  ability  to  grow  under  sometimes 
unfavorable  conditions,  are  called  weeds. 
Such  plants  —  the  dandelion,  butter  and 
eggs,  the  shepherd's  purse  —  are  particu- 
larly well  fitted  by  nature  'to  produce 
many  of  their  kind,  and  by  this  means 
drive  out  other  plants  which  cannot  do 
this  so  well.  On  these  or  other  plants 
we  find  feeding  several  kinds  of  animals, 
usually  insects. 

If  we  attempt  to  compare,  for  example, 
a  grasshopper  with  the  plant  on  which  it 
feeds,  we  see  several  points  of  likeness  and 
difference  at  once.  Both  plant  and  insect 
are  made  up  of  parts,  each  of  which,  as 
the  stem  of  the  plant  or  the  leg  of  the 
insect,  appears  to  be  distinct,  but  which  is 
a  part  of  the  whole  living  plant  or  animal. 
Each  part  of  the  living  plant  or  animal 
which  has  a  separate  work  to  do  is  called  an  organ.  Thus  plants 
and  animals  are  spoken  of  as  living  organisms. 

Functions  of  the  Parts  of  a  Plant.  —  We  are  all  familiar  with 
the  parts  of  a  plant,  —  the  root,  stem,  leaves,  flowers,  and  fruit. 

26 


A  Weed.  Notice  the  un- 
favorable habitat.  Pho- 
tograph by  W.  A.  Bar- 
bour. 


COMPOSITION   OF  LIVING   THINGS 


27 


But  we  may  not  know  so  much  about  their  uses  to  the  plant.  Each 
of  these  structures  differs  from  every  other  part,  and  each  has  a 
separate  work  or  function  to  perform 
for  the  plant.  The  root  holds  the  plant 
firmly  in  the  ground  and  takes  in  water 
and  mineral  matter  from  the  soil;  the 
stem  holds  the  leaves  up  to  the  light  and 
acts  as  a  pathway  for  fluids  between  the 
root  and  leaves;  the  leaves,  under  cer- 
tain conditions,  manufacture  food  for 
the  plant  and  breathe;  the  flowers  form 
the  fruits;  the  fruits  hold  the  seeds, 
which  in  turn  hold  young  plants  which 
are  capable  of  reproducing  adult  plants 
of  the  same  kind. 

The  Functions  of  an  Animal.  —  If 
we  examine  the  grasshopper  more 
carefully,  we  find  that  it  has  a  head, 
a  jointed  body  composed  of  a  middle 
and  a  hind  part,  three  pairs  of  jointed 
legs,  and  two  pairs  of  wings.  Obvi- 
ously, the  wings  and  legs  are  used  for  movement;  a  careful 
watching  of  the  hind  part  of  the  animal  shows  us  that  breathing 
movements  are  taking  place;  a  bit  of  grass  placed  before  it  may 
be  eaten,  the  tiny  black  jaws  biting  little  pieces  out  of  the  grass. 
If  disturbed,  the  insect  hops  away,  and  if  we  try  to  get  it,  it 
jumps  or  flies  away,  evidently  seeing  us  before  we  can  grasp  it. 
Hundreds  of  little  grasshoppers  indicate  that  the  grasshopper  can 
reproduce  its  own  kind,  but  in  other  respects  the  animal  seems 
quite  unlike  the  plant.  The  animal  moves,  breathes,  feeds,  and 
has  sensation,  while  apparently  the  plant  does  none  of  these.  It 
will  be  the  purpose  of  later  chapters  to  prove  that  the  functions 
of  plants  and  animals  are  in  many  respects  similar  and  that  both 
plants  and  animals  breathe,  feed,  and  reproduce. 

Organs.  —  If  we  look  carefully  at  the  organ  of  a  plant  called  a 
leaf,  we  find  that  the  materials  of  which  it  is  composed  do  not  ap- 
pear to  be  everywhere  the  same.  The  leaf  is  much  thinner  and 
more  dehcate  in  some  parts  than  in  others.     Holding  the  flat,  ex- 


Section  through  the  blade  of  a 
leaf,  as  seen  under  the  com- 
pound microscope ;  iS,  air 
spaces,  which  communicate 
with  the  outside  air;  V,  vein 
in  cross  section  ;  ST,  breath- 
ing hole ;  E,  outer  layer  of 
cells;  P,  green  cells. 


28  COMPOSITION  OF  LIVING  THINGS 

panded  blade  away  from  the  branch  is  a  Uttle  stalk,  the  petiole, 
which  extends  into  the  blade  of  the  leaf.  Here  it  splits  up  into  a  net- 
work of  tiny  veins  which  evidently  form  a  framework  for  the  flat 
blade  somewhat  as  the  sticks  of  a  kite  hold  the  paper  in  place.  If 
we  examine  under  the  compound  microscope  a  thin  section  cut 
across  the  leaf,  we  shall  find  that  the  veins  as  well  as  the  other  parts 
are  made  up  of  many  tiny  boxUke  units  of  various  sizes  and 
shapes.  These  smallest  units  of  building  material  of  the 
plant  or  animal  disclosed  by  the  compound  microscope  are  called 
cells.  The  organs  of  a  plant  or  animal  are  built  of  these  tiny 
structures. 

Tissues.  —  The  cells  which  form  certain  parts  of  the  veins,  the 
flat  blade,  or  other  portions  of  the  plant,  are  often  found  in  groups 
or  collections,  the  cells  of  which  are  more  or  less  alike  in  size  and 
shape.  Such  a  collection  of  cells  is  called  a  tissue.  Examples 
of  tissues  are  the  cells  covering  the  outside  of  the  human  body, 
the  muscle  cells,  which  collectively  allow  of  movement,  bony 
tissues  which  form  the  framework  to  which  the  muscles  are  at- 
tached, and  many  others. 

Adaptations  of  Structure  to  Function.  —  If  I  look  at  my  hand 
as  I  write,  I  notice  that  the  fingers  of  my  right  hand  grasp 
the  pen  firmly;  that  because  of  the  several  joints  in  the  fingers, 
the  wrist,  and  forearm,  free  movement  can  be  given  to  the  hand 
when  the  muscles  attached  to  the  bones  move  it.  The  hand  is 
capable  of  a  great  number  of  complicated  and  delicate  move- 
ments, most  of  them  associated  with  the  work  of  grasping  objects. 
Because  of  the  peculiar  fitness  in  the  structure  of  the  hand  for 
this  work,  we  say  that  it  is  adapted  to  this,  its  function,  that  is, 
grasping  objects.  Each  organ  of  the  plant  is  fitted  or  adapted  in 
some  way  to  do  certain  kinds  of  work.  It  is  the  object  of  the 
chapters  following  to  point  out  how  the  parts  of  a  plant  or  animal 
are  adapted  to  their  various  functions. 

Problem  V,  The  structure  and  general  properties  of  living 
matter.    {Laboratory  Manual,  Proh.  F.) 

To  the  Teacher.  —  Any  simple  plant  or  animal  tissue  can  be  used  to  demon- 
strate the  cell.  Epidermal  cells  may  be  stripped  from  the  body  of  the  frog 
or  obtained  by  scraping  the  inside  of  one's  mouth.     The  thin  skin  from 


COMPOSITION   OF   LIVING   THINGS 


29 


an  onion  shows  well,  as  do  thin  sections  of  a  young  stem,  as  the  bean  or 
pea.  I  have  found  one  of  the  best  places  to  study  a  tissue  and  the  cells 
of  which  it  is  composed  in  the  leaf  of  a  green  water  plant,  Elodea.  In  this 
plant  the  cells  are  lai^e,  and  not  only  the  outline  of  the  cells,  but  the  move- 
ment of  the  living  matter  within  the  cells,  may  easily  be  seen,  and  most 
of  the  parts  described  in  the  next  paragraph  can  be  demonstrated. 

Cells.  —  A  cell  may  he  defined  as  a  tiny  mass  of  living  matter,  either 
living  alone  or  forming  the  building  material  of  a  living  thing.  The 
living  matter  of  which  all  cells  are  formed  is  known  as  protoplasm 
(from  two  Greek  works  meaning  first  form).  When  viewed  under  a 
high  magnification  of  a  compound  microscope,  it  is  a  grayish,  semi- 
fluid mass,  seemingly  almost  devoid  of  any  structure.  A  careful 
observer  will  find,  however,  that  the  material  seems  to  be  made  of 
a  ground  mass  of  fluid  Avith 
innumerable  granules  of 
various  size  and  form  float- 
ing in  the  fluid  portion. 
All  plant  and  animal  cells 
appear  to  be  alike  in  the 
fact  that  every  living  cell 
possesses  a  structure 
known  as  the  nucleus  (pi. 
nuclei),  which  is  found 
within  the  body  of  the  ceil. 

The  nucleus  is  composed  of 
hving  matter  like  the  rest  of 
the  cell,  although  it  seems  to 
differ  in  some  chemical  way 
from  that  part  of  the  cell  sur- 
rounding it.  This  is  seen 
when  a  plant  or  animal  is 
placed  in  a  liquid  containing 
some  dye  such  as  logwood. 
Certain  bodies  in  the  nucleus 
take  up  the  stain  much  more 
readily  than   the  rest  of  the 

living  matter  of  the  cell,  taking  on  a  deep  black  color, 
called  the  chromosomes  (color-bearing  bodies). 

The  chromosomes,  which  are  believed  to  be  always  definite  in  number  for 
every  tissue  cell,  are  of  much  interest  to  scientists.     It  is  found  that  each 


Diagram  of  a  cell  (after  Wilson).  The  cell 
protoplasm  contains  spaces  to  hold  liquid  cell 
sap  {C.8.) ;  just  above  the  nucleus  {N.l.)  is 
a  structure  called  the  centrosome  (c),  which 
aids  in  cell  division ;  within  the  nucleus  are 
chromosomes  (N.n.),  which  form  a  network; 
t.n.,  nucleolus ;  Cp.,  plastids;  C.f.,  lifeless 
material  in  the  cell. 


They  are  thus 


30 


COMPOSITION   OF   LIVING  THINGS 


time  a  cell  splits  to  form  two  new  cells,  each  chromosome  splits  length- 
wise and  the  parts  go  in  equal  numbers  into  the  nucleus  of  each  of  the  two 
new  cells  thus  formed.  These  chromosomes  are  supposed  to  be  the  bearers 
of  the  qualities  which  we  believe  can  be  handed  down  from  plant  to  plant 
and  from  animal  to  animal ;  in  other  words,  the  inheritable  qualities  which 
make  the  offspring  like  its  parents. 

The  bulk  of  the  nucleus  is  filled  with  a  fluid,  and  in  some  nuclei  a  body 
known  as  a  nucleolus  is  found  ;  it  does  not,  however,  seem  to  be  a  constant 
structure.     The  protoplasm  surrounding  the  nucleus  is  called  cytoplasm. 

The  protoplasm  in  some  cells  collects  into  little  bodies  called  plastids. 
In  plant  cells  the  plastids  are  frequently  colored  green.  This  green  color- 
ing matter,  which  is  found  only  in  plant  cells,  is  called  chlorophyll,  and 
green  plastids  are  called  chlorophyll  bodies.  The  cytoplasm  of  a  cell  con- 
tain spaces,  which  are  usually  filled  with  a  fluid  known  as  cell  sap.  These 
spaces  in  the  cytoplasm  are  given  the  name  of  vacuoles.  Frequently  non- 
living materials  are  found  within  the  cytoplasm  of  the  cell. 

The  cell  is  surrounded  by  a  very  delicate  living  structure  called  the 
cell  membrane.  Outside  this  membrane  a  wall  is  formed  by  the  activity 
of  the  protoplasm  in  the  cells  of  plants.     These  cell  walls  form  wood. 

How  Cells  form  Others.  —  Cells  grow  to  a  certain  size  and  then 
split  into  two  new  cells.     In  this  process,  which  is  of  very  great 

importance  in  the 
growth  of  both  plants 
and  animals,  the  nucleus 
divides  first.  The 
chromosomes  also  di- 
vide, each  splitting 
lengthwise  and  the 
parts  going  in  equal 
numbers  to  each  of  the 
two  cells  formed  from 
the  old  cell.  Lastly, 
the  cytoplasm  sepa- 
rates, and  two  new  cells 
are  formed.  This  pro- 
cess is  known  as  fission.  It  is  the  usual  method  of  growth  found 
in  the  tissues  of  plants  and  animals. 


Stages  in  the  division  of  one  cell  to  form  two  cells. 
Note  the  separation  of  the  chromosomes  in  the 
nucleus.     Which  part  of  the  cell  divides  first  ? 


Cells  of  Various  Sizes  and  Shapes.  —  Plant  cells  and  animal  cells  are 
of  very  diverse  shapes  and  sizes.  There  are  cells  so  large  that  they  can 
easily  be  seen  with  the  unaided  eye ;  for  example,  the  root  hairs  of  plants 


COMPOSITION  OF  LIVING   THINGS  31 

and  eggs  of  some  animals.  On  the  other  hand,  cells  may  be  so  minute  that 
in  the  case  of  the  plant  cells  named  bacteria,  several  million  could  be  placed 
on  the  dot  of  this  letter  i.  The  forms  of  cells  may  be  extremely  varied  in 
different  tissues ;  they  may  assume  the  form  of  cubes,  columns,  spheres, 
flat  plates,  or  may  be  extremely  irregular  in  shape.  One  kind  of  tissue 
cell,  found  in  man,  has  a  body  so  small  as  to  be  quite  invisible  to  the  naked 
eye,  although  it  has  a  prolongation  several  feet  in  length.  Such  are  some 
of  the  cells  of  the  nervous  system  of  man  and  other  large  animals,  as  the 
ox,  elephant,  and  whale. 

Varying  Sizes  of  Living  Things.  —  Plant  cells  and  animal  cells  may 
live  alone  or  they  may  form  collections  of  cells.  Some  plants  are  so  simple 
in  structure  as  to  be  formed  of  only  one  kind  of  cells.  Usually  living 
organisms  are  composed  of  several  groups  of  different  kinds  of  cells.  It  is 
only  necessary  to  call  attention  to  the  fact  that  such  collections  of  cells 
may  form  organisms  so  tiny  as  to  be  barely  visible  to  the  eye ;  as,  for  in- 
stance, some  water-loving,  flowerless  plants  or  many  of  the  tiny  animals 
living  in  fresh  water  or  salt  water,  such  as  the  hydra,  small  worms,  and  tiny 
crustaceans.  On  the  other  hand,  among  animals  the  bulk  of  the  elephant 
and  whale,  and  among  plants  the  big  trees  of  California,  stand  out  as  no- 
table examples. 

Relation  to  Organic  and  Inorganic  Matter.  —  The  inorganic 
matter  covering  the  earth,  as  air  and  water,  and  forming-  the  great 
mass  of  its  bulk,  is  made  use  of  by  plants  and  animals.  The  latter 
make  their  homes  in  earth,  air,  or  water ;  they  take  in  the  oxygen 
of  the  atmosphere;  they  use  the  water  for  drinking;  but  in  the 
main  their  food  consists  of  organic  matter.  Plants,  on  the  other 
hand,  manufacture  food  out  of  the  dead  organic  and  inorganic 
matter  contained  in  the  soil,  air,  and  water,  and  then  change  this 
food  into  the  living  matter  of  their  own  bodies.  This  organic 
matter  in  turn  may  become  food  for  animals. 

In  the  last  chapter  we  found  that  the  classes  of  substances  in 
an  animal  or  plant  and  the  organic  food  substances  have  a  similar 
composition.  Let  us  now  consider  chemically  the  substance  which 
forms  the  basis  of  all  living  things. 

Chemical  Composition  of  Protoplasm.  —  Living  matter,  when 
analyzed  by  chemists  in  the  laboratory,  seems  to  have  a  very  com- 
plex chemical  composition.  It  is  somewhat  like  a  proteid  in  that 
it  always  contains  the  element  nitrogen.  It  also  contains  the  ele- 
ments carbon,  hydrogen,  oxygen,  and  a  little  sulphur.  Calcium, 
iron,  silicon,  sodium,  potassium,  phosphorus,  and  other  mineral 


32  COMPOSITION   OF   LIVING   THINGS 

matters  are  usually  found  in  very  niinute  quantities  in  its  com- 
position. We  believe  that  the  matter  out  of  which  plants  and 
animals  are  formed,  although  a  very  complex  building  material 
and  almost  impossible  of  correct  analysis,  is  composed  of  the 
above-named  elements.  What  is  of  far  more  importance  to  us 
is  the  fact  that  it  is  distinguished  by  certain  properties  which  it 
possesses  and  which  inorganic  matter  does  not  possess. 

Properties  of  Protoplasm.  —  The  properties  of  protoplasm  are 
as  follows :  — 

(1)  It  responds  to  influences  or  stimulation  from  without  its 
own  substance.  Both  plants  and  animals  are  sensitive  to  touch 
or  stimulation  by  light,  heat,  or  electricity.  One  of  the  simplest 
forms  of  plant  life,  the  slime  mold,  a  mass  of  naked  protoplasm,  if 
placed  on  a  damp  blotting  paper,  moistened  at  one  end  with  an 
infusion  of  leaves,  and  at  the  other  \^4th  a  solution  of  quinine,  \nll 
crawl  to  that  part  of  the  blotter  most  like  its  habitat,  that  is,  moist 
leaves.  Leaves  turn  toward  the  source  of  Hght.  Some  animals 
are  attracted  to  light  and  others  repelled  by  it ;  the  earthworm  is 
an  example  of  the  latter.      Protoplasm  is  thus  said  to  be  irriiabb 

(2)  Protoplasm  has  the  pouter  to  move  and  to  contract.  Muscular 
movement  is  a  familiar  instance  of  this  power.  Plants  move  their 
leaves  and  other  organs. 

(3)  Protoplasm  has  the  power  of  taking  up  food  materials,  of  se- 
lecting the  materials  which  can  be  used  by  it,  and  of  rejecting  the  sub- 
stances that  it  cannot  use.  A  commercial  sponge,  the  dried  skeleton 
of  an  animal,  if  placed  in  water,  will  swell  up  with  the  water  ab- 
sorbed by  it,  but  the  water  thus  taken  in  is  not  used  by  the  dead 
skeleton.  Protoplasm,  however,  in  the  tiny  projections  of  the  root 
called  root  hairs,  takes  in  only  the  material  which  ^vill  l>e  of  use 
in  forming  food  or  new  protoplasm  for  the  plant.  An  animal 
absorbs  into  its  body  only  food  material  that  can  be  used,  reject- 
ing material  unfit  for  food. 

(4)  Protoplasm  grows,  not  as  inorganic  objects  grow,  from  the  outside , ' 
btU  by  a  process  of  taking  in  food  material  and  then  changing  it 
into  living  material.     To  do  this  it  is  evident  that  the  same  chem- 

*  Home  Experiment.  —  Make  a  strong  solution  of  alum  (two  spoonfuls  of  pow- 
dered alum  to  half  a  glass  of  water).  Suspend  in  the  solution  a  thread  with  a  pebble 
attached  to  the  lower  end.     Notice  where  and  how  crystals  of  alum  grow. 


COMPOSITION  OF  LIVING   THINGS  33 

loal  elements  must  enter  into  the  composition  of  the  food  sub- 
stances as  are  found  in  ii\'ing  matter.  The  simplest  plants  and 
animals  have  tliis  wonderful  power  as  certainly  developed  as  the 
most  complex  forms  of  life. 

(5)  Protoplasm^  be  iiin  the  body  of  a  plant  or  of  an  animaly  uses 
oxygen.  It  breathes.  Thus  substances  taken  into  the  body  are 
oxidized,  and  release  energ>'  for  movement  and  the  other  activi- 
ties of  plants  and  animals. 

(6)  Protoplasm  has  the  power  to  rid  itself  of  waste  materials, 
especially  those  which  might  be  hannful  to  it.  A  tree  sheds  its 
leaves,  and  as  a  result  gets  rid  of  the  accumulation  of  mineral  matter 
in  the  leaves.  Plants  and  aninuAt  alike  pass  off  the  carbon  dioxide 
which  results  from  the  verj'  prooeaBes  of  living,  the  oxidation  of 
p>arts  of  their  own  bodies.  Animals  eliminate  wastes  containing 
nitrogen  through  the  skin  and  the  kidneys. 

(7)  Protoplasm  can  reproduce^  that  is,  form  other  matter  Hke  iUdJ. 
New  plants  are  constantly  appearing  to  take  the  places  of  those 
tliat  die.  The  supply  of  U\'ing  thingiB  upon  the  earth  is  not  de- 
creasing; reproduction  is  constantly  taking  place.  In  a  general 
way  it  is  possible  to  say  that  plants  and  animals  reproduce  in  a 
very  similar  manner.     We  shall  study  this  more  in  detail  later. 

To  sum  up,  we  find  that  living  protoplasm  has  the  properties 
of  sensibility,  motion,  groii'th,  and  reproduction  alike  in  its  sim- 
plest state  as  a  one-celled  plant  cr  animal  and  as  it  enters  into 
the  composition  of  a  hi^y  complex  organism  such  as  a  tree,  a 
dog,  or  a  man. 

Books  pob  RBFrnxmca 


Shaipe,  A  LabanUorii  MamMoL    American  Book  Company. 

Atkinson.  Fint  SUtdiet  nf  PlatU  Life.    Chap.  XI.     Ginn  and  Company. 

Snj-der.  The  Ckemutir^  ^ PImd  ami  Ammai  Life.    Tlie  Macmillun  Company. 


Coulter.  Barnes,  and  Caf«leB.iirei««ift</Boiniy.  Part  IL    American  Book  C< 

pany. 
Goodale.  Pk^tiotogieat  Botamff.    American  Book  Company. 
Green.  V^ehAk  Phmiolt&M-    J.  and  A.  ChurefailL 

Parker.  An  Blemenlary  Cemr^  in  Proeticat  Biologw-    Tlie  Macmillan  Company. 
Sedgwick  and  Wilson.  Genend  Biolon.    Henry  Holt  and  Company. 
Verrora.  Gmeral  PJkymblogy.    The  Macmillan  Company. 
Wilson,  The  C<U  ia  Dewelopmteni  amd  Inkeritmmee.    The  Marmillan  Company. 
HUNT.  B8.  BIO. 3 


rV.   FLOWERS  AND  THEIR  WORK 


Problem  VI,  The  structure  and  worh  of  the  parts  of  a 
flower.    {Laboratory  Manual,  Proh.  VI.) 

Structure  of  a  Simple  Flower.  —  Flowers  of  different  kinds  of 
plants  vary  greatly  in  size,  shape,  and  color.  In  our  study  of  the 
flower  our  problem  will  be  primarily  to  find  out  the  use  of  the 
flower  to  the  plant  which  produces  it.  To  solve  this  problem  we 
must  first  learn  something  of  the  structure  and  uses  of  the  parts 

of  a  very  simple  flower.  Examples  of 
such  flowers  are  the  evening  primrose 
and  the  sedum  (live-forever),  both  of 
which  are  plentiful  in  the  fall. 

The  Floral  Envelope.  —  In  such  a 
flower  the  expanded  portion  of  the 
flower  stalk,  which  holds  the  parts  of 
the  flower,  is  called  the  receptacle. 
The  jive  green  leaflike  parts  covering 
the  unopened  flower  are  called  the  sepals. 
Sometimes  the  sepals  are  all  joined  or 
united  in  one  piece.  Taken  together, 
they  are  called  the  calyx.  The  sepals 
come  out  in  a  circle  or  whorl  on  the 
flower  stalk. 

The  more  brightly  colored  structures 
are  the  petals.  They  form  the  corolla. 
The  corolla  is  of  importance,  as  we  shall  see  later,  in  making 
the  flower  conspicuous. 

The  Essential  Organs. —  A  flower,  however,  could  live  without 
sepals  or  petals  and  still  do  the  work  for  which  it  exists.  The 
essential  organs  of  the  flower  are  within  the  so-called  floral  en- 
velope.   They  consist  of  the  stamens  and  carpels  (or  pistil),  the 

34 


A  flower  of  the  sedum,  from  the 
side,  considerably  enlarged ; 
A,  anther  of  stamen ;  C,  car- 
pel; F,  filament;  P,  petal; 
S,  sepal. 


FLOWERS  AND   THEIR   WORK 


35 


A  flower  of  the  sedum  from 
above;  A,  anther;  C,  carpel; 
F,  lament ;  P,  petal ;  5,  sepal. 
Notice  how  the  parts  come 
out  in  circles  or  whorls. 


latter  being  in  the  center  of  the  flower.  The  structures  with  the 
knobbed  ends  are  called  stamens.  In  a  single  stamen  the  boxlike 
part  at  the  end  is  the  anther;  the  stalk  is  called  the  filament.  The 
anther  is  in  reality  a  hollow  box  which  produces  a  largo  number  of 
little  grains  called  'pollen.  It  is  neces- 
sary for  the  reproduction  of  new  plants 
that  the  pollen  get  out  of  the  anther. 
Each  carpel  or  pistil  is  composed  of  a 
rather  stout  base  called  the  ovary y  and 
a  more  or  less  lengthened  portion  rising 
from  the  ovary  called  the  style.  The 
upper  end  of  the  style,  which  in  some 
cases  is  somewhat  broadened,  is  called 
the  stigma.  The  stigmatic  surface 
usually  secretes  a  sweet  fluid  in  which 
grains  of  pollen  from  flowers  of  the 
same  kind  can  grow. 

Pollen.  —  Pollen  grains  of  various 
flowers,  when  seen  under  the  micro- 
scope, diff'er  greatly  in  form  and  appearance.  Some  are  rela- 
tively large,  some  small,  some  rough,  others  smooth,  some  spherical, 
and  others  angular.     They  all  agree,  however,  in  having  a  thick 

wall,  with  a  thin  membrane  under 
it,  the  whole  inclosing  a  mass  of 
protoplasm.  At  an  early  stage  the 
I^ollen  grain  contains  but  a  single 
cell.  When  we  see  it,  however,  we 
can  distinguish  two  nuclei  in  the 
protoplasm.  Hence  we  know  that 
at  least  two  cells  exist  there. 

Growth  of  Pollen  Grains.  —  Under 
certain  conditions  a  pollen  grain  will 
burst  open  and  grow.  This  growth 
can  be  artificially  produced  in  the 
laboratory  by  sprinkling  pollen  from  well-opened  flowers  of 
sweet  pea  or  nasturtium  on  a  solution  of  15  parts  of  sugar  to 
100  of  water.  Left  for  a  few  hours  in  a  warm  and  moist  place 
and  then  examined  under  the  microscope,  the  grains  of  pollen  will 


I 

n 

A  pollen  grain  highly  magnified. 
It  contains  two  nuclei  (n,  n')  at 
the  stage  here  represented. 


36 


FLOWERS  AND   THEIR  WORK 


be  found  to  have  germinated,  a  long,  threadlike  mass  of  protoplasm 
growing  from  it  into  the  sugar  solution.  The  presence  of  this 
sugar  solution  was  sufficient  to  induce  growth.  When  the  pollen 
grain  germinates,  one  of  the  nuclei  enters  the  threadlike  growth 
(this  growth  is  called  the  pollen  tube;  see  Figure).  The  cell 
which  grows  into  the  pollen  tube  is  known  as  the  sperm  cell. 

Fertilization  of  the  Flower.  —  If  we  cut  the  pistil  of  a  large 
flower  (as  a  lily)  lengthwise,  we  notice  that  the  style  appears  to  be 

composed  of  rather  spongy 
material  in  the  interior; 
the  ovary  is  hollow  and  is 
seen  to  contain  a  num- 
ber of  rounded  structures 
which  appear  to  grow  out 
from  the  wall  of  the  ovary. 
These  are  the  ovules.  The 
ovuleS)  under  certain  con- 
ditions, become  seeds.  An 
explanation  of  these  con- 
ditions may  be  had  if  we 
examine,  under  the  micro- 
scope, a  very  thin  section 
of  a  pistil,  on  which  pollen 
has  begun  to  germinate.  The  central  part  of  the  style  is  found 
to  be  either  hollow  or  composed  of  a  soft  tissue  through  which 
the  pollen  tube  can  easily  grow.  Upon  germination,  the  pollen 
tube  grows  downward  through  the  spongy  center  of  the  style,  fol- 
lows the  path  of  least  resistance  to  the  space  within  the  ovary,  and 
there  enters  the  ovule.  It  is  beUeved  that  some  chemical  influence 
thus  attracts  the  pollen  tube.  When  it  reaches  the  ovary,  the 
sperm  cell  penetrates  an  ovule  by  making  its  way  through  a  little 
hole  called  the  micropyle.  It  then  grows  toward  a  clear  bit  of  proto- 
plasm known  as  the  embryo  sac.  The  embryo  sac  is  an  ovoid  space, 
microscopic  in  size,  filled  with  semifluid  protoplasm  containing  sev- 
eral nuclei.  (See  Figin-e.)  One  of  the  nuclei,  with  the  protoplasm 
immediately  surrounding  it,  is  called  the  egg  cell.  It  is  this  cell  that 
the  sperm  cell  of  the  pollen  tube  grows  toward;  ultimately  the 
sperm  cell  reaches  the  egg  cell  and  unites  with  it.      The  two  cells, 


Three  stages  in  the  germination  of  the  pollen 
grains  ;  one  of  the  nuclei  in  (3)  is  the  sperm 
cell  nucleus.  Drawn  under  the  compound 
microscope. 


FLOWERS  AND  THEIR  WORK 


37 


after  coming  together,  unite  to  form  a  single  cell.  This  process 
is  known  as  fertilization.  This  single  cell  formed  by  the  union 
of  the  pollen  tube  cell  or  sperm  and  the  egg  cell  is  now  called 
a  fertilized  egg. 

Development  of  Ovule  into  Seed.  —  The 
primary  reason  for  the  existence  of  a  flower 
is  that  it  fnay  produce  seeds  from  which  future 
plants  will  graw.  The  first  beginning  of  the 
growth  of  the  seed  takes  place  at  the  mo- 
ment of  fertilization.  From  that  time  on 
there  is  a  growth  within  the  ovule  of  a  lit- 
tle structure  called  the  embryo.     The  embryo 

will  give  rise  to  the  future  plant.     After  ferti-  I     I 

lization  the  ovule  grows  into  a  seed. 

Problem  VII.  A  study  of  cross-pollina- 
tion and  some  means  of  bringing  it  about. 
(Laboratory  Manual,  Prob.  VII.) 

(a)  Adaptations  in  tlie  flower. 

(b)  Adaptations  in  an  insect  agent. 

(c)  Other  agents. 


History  of  the  Discoveries  regarding  Pol- 
lination of  Flowers.  —  Although  the  ancient 
Greek  and  Roman  naturalists  had  some 
vague  ideas  on  the  subject  of  fertilization, 
it  was  not  until  the  latter  part  of  the  eight- 
eenth century  that  it  was  demonstrated  that 
pollen  was  necessary  for  the  growth  of  the 
embryo  within  a  seed.  In  the  latter  part 
of  the  eighteenth  century  a  book  appeared 
in  which  a  German  named  Conrad  Sprengel 
worked  out  the  facts  that  the  structure  of 
certain  flowers  seemed  to  be  adapted  to 
the  visits  of  insects.  Certain  facilities  were 
offered  to  an  insect  in  the  way  of  easy 
foothold,  sweet  odor,  and  especially  food  in 
the  shape  of  pollen  and  nectar,  the  latter 


Fertilization  of  the 
oviJe.  A  pistil  cut 
down  lengthwise  (only 
one  side  shown).  The 
pollen  tube  is  seen  en- 
tering the  cavity  (lo- 
cule)  of  the  ovary. 


38 


FLOWERS  AND  THEIR  WORK 


a  sweet-tasting  substance  manufactured  by  certain  parts  of  the 
flower  known  as  the  nectar  glands.  Sprengel  further  discov- 
ered the  fact  that  pollen  could  be  and  was  carried  by  the 
insect  visitors  from  the  anthers  of  the  flower  to  its  stigma. 
It  was  not  until  the  middle  of  the  nineteenth  century,  however, 
that  an  Englishman,  Charles  Darwin,  worked  out  the  true  relation 
of  insects  to  flowers  by  his  investigations  upon  the  cross-poUination 

of  flowers.  By  pollination  we 
mean  the  transfer  of  pollen  from 
an  anther  to  the  stigma  of  a 
flower.  Self-pollination  is  the 
transfer  of  pollen  from  the  an- 
ther  to  the  stigma  of  the  same 
flower;  cross-pollination  is  the 
transfer  of  pollen  from  the  an- 
thers of  one  flower  to  the  stigma 
of  another  flower  of  the  same 
kind.  Many  species  of  flowers 
are  self-pollinated  and  do  not 
do  so  well  in  seed  production 
if  cross-pollinated,  but  Charles 
Darwin  found  that  some  flowers 
which  were  self-pollinated  did 
not  produce  so  many  seeds, 
and  that  the  plants  which  grew 
from  their  seeds  were  smaller 
and  weaker  than  plants  from 
seeds  produced  by  cro^s-pol- 
linated  flowers  of  the  same 
kind.  He  also  found  that  plants  grown  from  cross-pollinated 
seeds  tended  to  vary  more  than  those  grown  from  self-pollinated 
seed.  This  has  an  important  bearing,  as  we  shall  see  later,  in  the 
production  of  new  varieties  of  plants.  Microscopic  examination 
of  the  stigma  at  the  time  of  pollination  also  shows  that  the  pollen 
from  another  flower  germinates  before  the  pollen  which  has  fallen 
from  the  anthers  of  the  same  flower.  This  latter  fact  alone  in  most 
cases  renders  it  unlikely  for  a  flower  to  produce  seeds  by  its  own 
pollen.     Darwin  worked  for  many  years  on  the  pollination  of  many 


A  wild  orchid,  a  flower  of  the  type  from 
which  Charles  Darwin  worked  out  his 
theory  of  cross-pollination  by  insects. 


FLOWERS  AND   THEIR   WORK 


insect-visited  flowers,  and  discovered  in  almost  every  case  that 
showy,  sweet-scented,  or  otherwise  attractive  flowers  were  adapted 
or  fitted  to  be  cross-pollinated  by  insects.  He  also  found  that,  in 
the  case  of  flowers  that  were  inconspicuous  in  appearance,  often  a 
compensation  appeared  in  the  odor  which  rendered  them  at- 
tractive to  certain  insects.  The  so-called  carrion  flowers,  pol- 
linated by  flies,  are  examples,  the  odor 
in  this  case  being  like  decayed  flesh. 
Other  flowers  open  at  night,  are  white, 
and  provided  with  a  powerful  scent  so 
as  to  attract  night-flying  moths  and 
other  insects.  Flowers  adapted  to 
be  cross-pollinated  by  insects  are  fre- 
quently irregular  in  shape.  Thus 
butter  and  eggs  is  a  flower  which  is 
well  fitted  for  cross-pollination  by  in- 
sects. 

Butter  and  Eggs  (Linaria  linaria).  — 
From  July  to  October  this  very  abundant 
weed  may  be  found  especially  along  road- 
sides and  in  sunny  fields.  The  flower 
cluster  forms  a  tall  and  conspicuous  flower 
cluster  known  as  a  spike,  the  yellow  and 
orange  flowers  being  arranged  so  that  they 
come  out  directly  from  the  main  flower 
stalk. 

The  corolla  projects  into  a  spur  on  tlie 
lower  side ;  an  upper  two-parted  lip  shuts 
down  upon  a  lower  three-parted  lip.     The 

four  stamens  are  in  pairs,  two  long  and  two  short.  (The  stamens  of 
two  lengths  are  so  placed  that  they  may  allow  self-pollination  in  stormy 
weather,  when  insects  fail  to  reach  the  flower.  The  instructor  should 
explain  this.) 

Certain  parts  of  the  corolla  are  more  brightly  colored  than  the 
rest  of  the  flower.  This  color  is  a  guide  to  insects.  Butter  and  eggs 
is  visited  most  by  bumblebees,  which  are  guided  by  the  orange  lip  to 
alight  just  where  they  can  push  their  way  into  the  flower.  The  bee, 
seeking  the  nectar  secreted  in  the  spur,  brushes  his  head  and  shoulders 
against  the  stamens.  Visiting  another  flower  of  the  cluster,  it  would 
be  an  easy  matter  accidentally  to  transfer  this  pollen  to  the  stigma  of 
finother  flower.     In  this  way  cross-pollination  is  effected. 


Spike    of    butter    and    eggs 
(linaria). 


40  FLOWERS   AND   THEIR  WORK 

Insects  as  Pollinating  Agents.^  —  No  one  who  sees  a  hive  of 
bees  with  their  wonderful  communal  life  can  fail  to  see  that  these 
insects  play  a  great  part  in  the  life  of  the  flowers  near  the  hive. 
A  famous  observer  named  Sir  John  Lubbock  tested  bees  and  wasps 
to  see  how  many  trips  they  made  daily  from  the  hive  to  the  flowers, 
and  found  that  the  wasp  went  out  on  116  visits  during  a  working  day 
of  16  hours,  while  the  bee  made  but  a  few  less  visits,  and  worked 
only  a  httle  less  time  than  the  wasp  worked.  It  is  evident  that 
in  the  course  of  so  many  trips  to  the  fields  a  bee  must  hght  on  and 
cross-pollinate  many  hundreds  of  flowers. 

Study  of  a  Bee.  —  The  body  of  a  bee  (and  of  all  other  insects) 
is  divided  into  three  parts.     Attached  to  the  middle  part  (the 


Bumblebees ;   a,  queen ;   b,  worker ;   c,  drone. 

thorax)  are  three  pairs  of  jointed  legs  and  two  pairs  of  tiny  wings. 
By  the  legs  and  the  jointed  body  we  are  able  to  distinguish  insects 

1  Suggestions  for  Field  Work.  —  At  this  point,  at  least  one  field  trip  should  be 
introduced  for  the  purpose  of  studying  under  natural  conditions  the  cross-pollina- 
tion of  flowers  by  insects.  For  suggestions  for  such  a  trip,  see  Hunter  and  Valentine, 
Manual,  page  207.  Many  of  the  following  exercises  on  fall  flowers  may  profitably 
be  taken  in  the  field  and  reported  on  by  the  pupil  as  class  exercises.  Excellent  sug- 
gestions for  a  field  trip  may  be  found  in  Andrews,  Botany  All  the  Year  Round.  To 
make  such  a  trip  successful,  the  teacher  should  first  know  the  locality  and  should 
have  directions  in  the  hands  of  each  pupil  before  starting.  Flowers  which  are  abim- 
dant  in  the  fall  and  which  show  adaptations  easily  worked  out  by  pupils  are  the 
evening  primrose  (Onagra  biennis),  moth  mullein  (Verbascum  blattaria),  and  jewel 
weed  (Impatiens  biflora). 

Directions  for  work  on  these  forms  and  for  a  field  trip  will  be  found  in  the  Labo- 
ratory Manual,  Prob.  VJJ. 


FLOWERS  AND   THEIR   WORK  41 

from  other  animals.  If  we  look  closely  at  the  bee,  we  find  the 
body  and  legs  more  or  less  covered  with  tiny  hairs ;  especially  are 
these  hairs  found  on  the  legs.  When  a  plant  or  animal  structure  is 
fitted  to  do  a  certain  kind  of  work,  we  say  it  is  adapted  to  do  that  work. 
The  joints  in  the  leg  of  the  bee  fit  it  for  complicated  movements; 
the  arrangement  of  stiff  hairs  along  the  edge  of  a  concavity  in  one 
of  the  joints  of  the  lv»g  forms  a  structure  well  fitted  to  hold  pollen. 
In  this  way  pollen  is  collected  by  the  bee  and  taken  to  the  hive  to  be 
used  as  food.  But  while  gathering  pollen  for  itself,  the  dust  is 
caught  on  the  hairs  and  other  projections  on  the  body  or  legs 
and  is  thus  carried  from  flower  to  flower.  Thus  cross-pollination 
may  be  effected. 

Pollination  not  intended  by  the  Bee.  —  The  cross-polH nation  of 
flowers  is  not  planned  by  the  bee ;  it  is  simply  an  incident  in  the 
course  of  the  food  gathering.  The  bee  visits  a  large  number  of 
flowers  of  the  same  species  during  the  course  of  a  single  visit  from 
the  hive,  and  it  is  then  that  cross-pollination  takes  place. 

Suggestions  for  Field  Work.  —  In  any  locality  where  flowers  are  abundant, 
try  to  answer  the  following  questions  :  How  many  bees  visit  the  locality 
in  ten  minutes  ?  How  many  other  insects  alight  on  the  flowers  ?  Do  bees 
visit  flowers  of  the  same  kinds  in  succession,  or  fly  from  one  flower  on 
a  given  plant  to  another  on  a  plant  of  a  different  kind  ?  If  the  bee  lights 
on  a  flower  cluster,  does  it  visit  more  than  one  flower  in  the  same  cluster  ? 
How  does  a  bee  alight  ?    Exactly  what  does  the  bee  do  when  it  alights  ? 

Is  Color  or  Odor  in  a  Flower  an  Attraction  to  an  Insect  ?  —  Try  to  decide 
whether  color  or  odor  has  the  most  effect  in  attracting  bees  to  flowers. 
Sir  John  Lubbock  tried  an  experiment  which  it  would  pay  a  number  of 
careful  pupils  to  repeat.  He  placed  a  few  drops  of  honey  on  glass  slips 
and  placed  them  over  papers  of  various  colors.  In  this  way  he  found  that 
the  honeybee,  for  example,  could  evidently  distinguish  different  colors. 
Bees  seemed  to  prefer  blue  to  any  other  color.  Flowers  of  a  yellow  or  flesh 
color  were  preferred  by  flies.  It  would  be  of  (jonsiderable  interest  for  some 
student  to  work  out  this  problem  with  our  native  bees  and  with  other 
insects.  Test  the  keenness  of  sight  in  insects  by  placing  a  white  object  (a 
white  golf  ball  will  do)  in  the  grass  and  see  how  many  insects  will  alight 
on  it.  Try  to  work  out  some  method  by  which  you  can  decide  whether  a 
given  insect  is  attracted  to  a  flower  by  odor  alone. 

The  Sight  of  the  Bumblebee,  —  The  large  eyes  located  on  the  sides  of 
the  head  are  made  up  of  a  large  number  of  little  units,  each  of  which  is 
considered  to  be  a  very  simple  eye.     The  large  eyes  are  therefore  called 


42 


FLOWERS  AND  THEIR  WORK 


the  compound  eyes.      All  insects  are  provided  with  compound  eyes,  with 
simple  eyes,  or,  in  most  cases,  with  both.     The  simple  eyes  of  the  bee  may 

be  found  by  a  careful  observer  be- 
tween and  above  the  compound  eyes. 
One  would  suppose  that  with  so 
many  eyes  the  sight  of  insects  would 
be  extremely  keen,  but  such  does 
not  seem  to  be  the  case.  Insects 
can,  as  we  have  already  learned,  dis- 
tinguish differences  in  color  at  some 
distance  ;  they  can  see  moving  ob- 
jects, but  they  do  not  seem  to  be 
able  to  make  out  form  well.  To 
make  up  for  this,  they  appear  to 
have  an  extremely  well-developed 
sense  of  smell.  Insects  can  distin- 
guish at  a  great  distance  odors  which 
to  the  human  nose  are  indistinguish- 
able. Night-flying  insects,  espe- 
cially, find  the 
A  lily  :  P,  petal ;  S,  stamen  (anther)  ;  flowers  by  the 
iS^P,  sepal;  5«,  pistil  (stigma).  Note  odor  rather 
the  nectar  guides  on  the  petals.  than  by  color. 


Nectar  and  Nectar  Glands.  —  The  bee  is 
attracted  to  a  flower  for  food.  This  food  may 
consist  of  pollen  or  nectar.  Nectar  is  a  sugary 
solution  that  is  formed  in  the  flower  by  little 
collections  of  cells  called  the  nectar  glands. 
The  nectar  glands  are  usually  so  placed  that 
to  get  to  them  the  insect  must  first  brush  the 
stamens  and  pistil  of  the  flower.  Frequently 
the  location  of  the  nectaries  (nectar  glands) 
is  made  conspicuous  by  brightly  colored 
markings  on  the  corolla  of  the  flower.  The 
row  of  dots  seen  in  the  tiger  lily  is  an  ex- 
ample. 


Head  of  the  bumble- 
bee ;  a,  antenna ;  g, 
tongue  used  in  lick- 
ing the  nectar  from 
flowers ;  m,  maxillae. 


Mouth  Parts  of  the  Bee The  mouth  of  the  bee  is  adapted  to  take  in 

the  foods  we  have  mentioned,  and  is  used  for  the  purposes  for  which  man 
would  use  the  hands  and  fingers.  The  honeybee  laps  or  sucks  nectar  from 
flowers,  it  chews  the  pollen,  and  it  uses  part  of  the  mouth  as  a  trowel  in 
making  the  honeycomb.     A  glance  at  the  Figure  shows  us  that  the  mouth 


FLOWERS  AND   THEIR   WORK 


43 


parts  of  the  bee  are  complex.  The  parts  consist  of  a  pair  of  very  small 
jaws  or  mandibles,  certain  other  structures,  maxUlce,  part  of  the  lower  lip 
called  the  labial  palps,  and 
a  long  tonguelike  structure 
called  the  ligula.  The  uses 
of  the  mouth  parts  may  be 
made  out  by  watching  a  bee 
on  a  well-opened  flower. 


/?//„.• 


a  flower. 


i>llinute 


Other  Flower  Visitors.' — 
Other  insects  besides  the 
bee  are  pollen  carriers  for 
flowers.  Among  the  most 
useful  are  moths  and  but- 
terflies. Both  insects  feed 
only  on  nectar,  which  they 
suck  through  a  long  tube- 
like proboscis.  The  heads  and  Ijodies  of  these  insects  are  more  or 
less  thickly  covered  with  hairs,  and  the  wings  are  thatched  with 
hairlike,  tiny  scales.    All  these  structures  are  of  use  to  the  flower 

because  they  collect  and 
carry  pollen.  Projecting 
from  each  side  of  the  head 
of  a  butterfly  is  a  fluff'y 
structure,  the  palp.  This 
collects  and  carries  a  large 
amount  of  pollen,  which  is 
deposited  upon  the  stig- 
mas of  other  flowers  when 
the  butterfly  pushes  its 
head  down  into  the  flower 
tube  after  nectar. 
Flies  and  some  other  insects  are  agents  in  cross-pollination. 
Humming  birds  are  also  active  agents  in  some  flowers.  Snails 
are  said  in  rare  instances  to  carry  pollen.  Man  and  the  domesti- 
cated animals  undoubtedly  frequently  pollinate  flowers  by  brush- 
ing past  them  through  the  fields. 

'  If  the  study  of  other  insects  is  taken  up  in  the  fall  in  connection  with  the  flower, 
the  student  sliould  be  referred  to  parts  of  Chapters  XX  and  XXI  and  to  the  Lab- 
oratory Manual. 


The  common  swallow-tailed  butterfly  on  clover. 
Bumblebees  usually  are  the  agents  which 
cross-pollinate  this  flower. 


44 


FLOWERS  AND   THEIR  WORK 


Cross-pollination  of  a  Head  (Clover).  —  In  a  flower  cluster  called  a 
head,  a  closely  massed  cluster  of  little  flowers  as  clover,  cross-pollination  is 
usually  effected  by  bumblebees  which  rapidly  work  from  one  flower  to 
another  in  the  same  cluster,  inserting  their  tongues  deep  into  the  flower 
cup.     The  butterfly  shown  in  the  illustration  inserts  its  proboscis  (seen 

curled  up  like  a  watch  spring  on  the  under- 
side of  the  head)  into  the  flower. 

Cross-pollination  of  a  Composite  Head. 
—  This  flower  cluster,  so  often  mistaken 
for  a  single  flower,  is  found  only  in  the 
great  Composite  family,  to  which  so  many 
of  our  commonest  flowers  and  weeds 
belong.  The  daisy,  aster,  goldenrod,  and 
sunflower  are  examples  of  the  Compositse. 
The  composite  head  is  well  seen  in  a 
daisy  or  the  sunflower.  This  head  has  an 
outer  circle  of  green  parts.  These  parts 
look  like  sepals,  but  in  reality  are  a  whorl 
of  leaflike  parts.  Taken  together  these 
form  an  involucre.  Inside  the  involucre 
is  a  whorl  of  brightly  colored,  irregular  flowers  called  the  ray  flowers. 
They  appear  to  act,  in  some  instances  at  least,  as  an  attraction  to  in- 
sects by  showing  a  definite  color  (see 
the  common  dogwood,  Cornus  florida). 
The  flowers  occupying  the  center  of 
the  cluster  are  the  disk  flowers.  Such 
a  flower  examined  under  the  hand 
lens  is  found  to  be  perfect.  A  care- 
ful observer  will  find  that  the  anthers 
are  united  in  a  ring  around  the  pistil. 
This  is  a  typical  condition  in  the  Com- 
positsB.     The  stamens  ripen  first  and 

grow  up  around  the  stigma,  which  ripens  later.  The  stigma  splits  (see  a), 
and  pollen  from  another  flower  brought  to  its  surface  will  germinate 
there. 


A  composite  head. 


Section  through  composite  head, 
showing  a  disk  flower  (a),  a  ray 
flower  (c),  and  the  involucre  (d). 


Other  examples. —  Many  other  examples  of  adaptations  to 
secm-e  cross-poUination  by  means  of  the  visits  of  insects  might  be 
given.  The  mountain  laurel,  which  makes  our  hillsides  so  beauti- 
ful in  late  spring,  shows  a  remarkable  adaptation  in  having  the 
stamens  caught  in  little  pockets  of  the  corolla.  The  weight  of 
the  visiting  insect  on  the  corolla  releases  the  anther  of  the  stamen 
from  the  pocket  in  which  it  rests,  and  the  body  of  the  visitor  is 
dusted  with  pollen. 


FLOWERS  AND   THEIR    WORK 


45 


Milkweed,  showing  the  flower  cluster  called  an 
umbel. 


The  milkweed  or  butterfly  weed  (Asdepias  cornuti)  is  another 
example  of  a  flower  adapted  to  insect  pollination.' 

Still  another  example  of 
cross-pollination  is  found 
in  the  yucca,  a  desert-lov- 
ing semitropical  lily  (to  be 
seen  in  most  botanic  gar- 
dens). In  this  flower  the 
stigmatic  surface  is  above 
the  anther,  and  the  pollen 
is  sticky  and  could  not  be 
transferred  except  by  in- 
sect aid.  This  is  accom- 
plished in  a  remarkable 
manner.     A   little   moth, 

called  the  pronuba,  gathers  pollen  from  an  anther,  flies  away  with 
this  load  to  another  flower,  there  deposits  an  egg  in  the  ovary  of  the 
pistil,  and  then  rubs  its  load  of  pollen  over  the 
stigma  of  the  flower.  The  young  hatch  out 
and  feed  on  the  young  seeds 
which  have  been  fertilized  by 
the  pollen  placed  on  the  stigma 
by  the  mother.  They  eat 
some  of  the  developing  seeds 
and  then  bore  out  of  the  seed 
pod  and  escape  to  the  ground, 
leaving  the  plant  to  develop 
the  remaining  seeds  without 
further  molestation. 

The  fig  insect  {Blastophaga 
grossoriim)  is  another  member 
of  the  insect  tribe  that  is  of 
considerable  economic  impor- 


Pod  of  yucca  pierced  by 
the  pronuba. 


Pronuba  polli- 
nating pistil  of 
yucca. 


I  For  an  excellent  account  of  cross-pollination  of  this  flower,  the  reader  is  re- 
ferred to  W.  C.  Stevens,  Introduction  to  Botany.  Orchids  are  well  known  to  botan- 
ists as  showing  some  very  wonderful  adaptations.  For  simple  reference  reading, 
see  Coultor,  Plant  Relations.  A  classic  easily  read  Is  Darwin,  On  the  Fertilization 
of  Orchids. 


46 


FLOWERS  AND   THEIR  WORK 


tance.  It  is  only  in  recent  years  that  the  fruit  growers  of  Cali- 
fornia have  discovered  that  the  fertilization  of  the  female  flowers 
is  brought  about  by  a  gallfly  which  bores  into  the  young  fruit.^ 
The  last  two  cases  are  only  some  of  the  many  examples  of  mutual 
help  among  plants  and  animals. 

Pollination  by  the  Wind.  —  Not  all  flowers  are  dependent  upon 
insects  for  cross-pollination.  Many  of  the  earliest  of  spring  flowers 
appear  almost  before  the  insects  do.  These  flowers,  needing  no 
conspicuous  colors  or  showy  corolla  to  attract  insects,  often  lack 

this  part  altogether. 
In  fact,  we  are  apt  en- 
tirely to  overlook  the 
flowers  which  appear 
in  the  spring  upon 
our  common  forest 
and  shade  trees.  In 
many  trees  the  flowers 
appear  before  the 
leaves  come  out.  Such 
flowers  are  dependent 
upon  the  wind  to 
carry  pollen  from  the 
stamens  of  one  flower 
to  the  pistil  of  an- 
other. Most  of  our 
common  trees,  oak, 
poplar,  maple,  and 
others,  are  cross-pol- 
linated almost  entirely 
by  the  wind. 

Among  the  adapta- 
tions that  a  wind-pollinated  flower  shows  are :  (1)  The  develop- 
ment of  very  many  pollen  grains  to  each  ovule.  In  one  of 
the  insect-pollinated  flowers,  that  of  the  night-blooming  cereus, 
the  ratio  of  pollen  grains  to  ovules  is  about  eight  to  one.  In 
flowers  which  are  to  be  pollinated  by  the  wind,  a  large  number 

1  The  teacher  is  referred  to  Yearbook  of  the  Department  of  Agriculture  for 
1900  for  data  on  the  insect  which  pollinates  the  Smyrna  fig. 


The  staminate  flower  of  the  corn.     Notice  the  hang- 
ing anthers  full  of  pollen. 


FLOWERS  AND   THEIR   WORK 


47 


of  the  pollen  grains  never  reach  their  destination  and  are 
wasted.  Therefore  in  such  plants  several  thousands,  perhaps 
hundreds  of  thousands,  of  pollen  grains  will  be  developed  to  every 
ovule  produced.  Such  are  the  pines.  In  May  and  early  June 
the  ground  under  pine  trees  is  often  yellow  with  pollen,  and  the 
air  may  be  filk^d  with  the  dust  for  miles  from  the  trees.  Such, 
also,  is  the  case  with  many  of  the  grasses. 

(2)  The  anthers  are  usually  exposed  to  the  wind  when  ripe. 
The  common  plantain  and  timothy  grass  are  excellent  examples. 

(3)  The  pistil  of  the  flower  is  peculiarly  fitted  to  retain  the  pollen 
by  having  feathery  projections  along  the  sides  which  increase  the 
stigmatic  surface.  This  can  be  seen  in  the  grass.  In  the  Indian 
corn  the  stigmatic  surface  is  the  so-called  silk  which  protrudes 
beyond  the  covering  of  modified  leaves  which  form  the  husk  of  the 
ear  of  corn.  All  our  grains,  wheat,  rye,  oats,  and  others,  have  the 
typical  feathery  pistil  of  the  wild  grasses  from  which  they  descended. 

(4)  The  corolla  is  often  entirely  lacking.  It  would  only  be  in  the 
way  in  flowers  that  are  dependent  upon  the  wind  to  carry  pollen. 

Imperfect  Flowers.  —  Some  flowers,  the  wind-pollinated  ones 
in  particular,  are  imperfect ;  that  is,  they  lack  either  stamens  or 
pistils.  In  such  flowers,  cross-polli- 
nation must  of  necessity  follow. 

If  only  the  staminate  flowers  (those 
which  contain  only  stamens)  are  developed 
on  one  plant,  and  only  the  pistillate  (those 
which  bear  only  pistils)  on  another,  we  call 
the  plant  dicecious.  A  common  example  is 
the  willow. 

Other  plants  bear  staminate  and  pistil- 
late flowers  on  the  same  plant.  In  this 
case  they  are  said  to  be  monoecious.  The 
oak,  hickory,  beech,  birch,  walnut,  and 
chestnut  are  familiar  examples. 

The  pine  tree  is  another  example  of  moncecious  tree;  the  male  or 
staminate  flowers  appear  in  tiny  clusters  called  catkins,  the  female  or 
pistillate  flowers  coming  a  little  later  as  tiny  cones,  which  in  most  species 
of  pines  take  nearly  two  years  to  produce  seeds. 

Water  Pollination.  —  An  unusual  method  of  pollination  is  found 
in  those  plants  which  live  almost  entirely  under  the  water.  In  eelgrass 
the  pistillate  flowers  are  attached  to  long,  slender  stalks  and  float  on  the 


Imperfect  flowers  of  the  squash, 
the  corolla  removed.  Pistil- 
late flower  at  the  left. 


48 


FLOWERS   AND   THEIR  WORK 


surface  of  the  water.  The  staminate  flowers,  when  ripe,  break  away  from 
their  submerged  stems  and  float  to  the  surface.  If  these  float  under  a 
pistillate  flower,  the  protruding  ends  of  the  pistils  catch  and  retain  some 
of  the  pollen  from  the  staminate  flower.  Thus  fertilization  follows. 
After  pollination,  the  stalk  of  the  pistillate  flower  coils  up  in  a  spiral  and 
draws  the  flower  under  the  surface  of  the  water,  so  that  the  seeds  may 
ripen  in  security. 

Summary.  —  If  we  now  collect  our  observations  upon  flowers 
with  a  view  to  making  a  summary  of  the  different  devices  flowers 


Flowers  of  the  Lady  Washington  geranium  showing  the  conditions  of  dichogamy ; 
A,  flower  with  stamens  ripe,  but  with  the  stigma  not  ready  to  receive  pollen ;  B, 
the  same  flower  at  a  later  stage ;  the  stamens  have  withered,  but  the  stigma  is  now 
ready  to  receive  pollen. 

have  assumed  to  prevent  self-pollination  and  to  secure  cross-pollina- 
tion, we  find  that  they  are  as  follows :  — 

(1)  The  stamens  and  pistils  may  be  found  in  separate  flowers, 
either  on  the  same  or  on  different  plants. 

(2)  The  stamens  may  produce  pollen  before  the  pistil  is  ready  to 
receive  it,  or  vice  versa.     This  condition  is  called  dichogamy. 

(3)  The  stamens  and  pistils  may  be  so  placed  with  reference  to  each 
other  that  pollination  can  be  brought  about  only  by  outside  assistance. 

In  some  flowers,  as  is  shown  by  the  primula  of  our  hothouses, 
the  stamens  and  pistils  are  each  of  two  different  lengths  in  different 


FLOWERS  AND   THEIR   WORK 


49 


Condition  of  stamens  and  pistils  in  the  spiked  loose- 
strife {Lythrum  aalicaria). 


flowers.  Short  styles  and  long  or  high-placed  filaments  are  found 
in  one  flower,  and  long  styles  with  short  or  low-placed  filaments  in 
the  other.  Pollination  will  be  eff'ected  only  when  some  of  the 
pollen  from  a  low-placed  anther  reaches  the  stigma  of  a  short- 
styled  flower,  or  when  the  pollen  from  a  high  anther  is  placed  upon 
a  long-styled  pistil. 
Flowers  which  have 
this  peculiar  condition 
are  said  to  he  dimorphic 
(Greek  =  of  two  forms). 
There  are,  as  in  the 
case  of  the  loosestrife, 
trimorphic  flowers 
having  pistils  and 
stamens  of  three 
lengths. 

Charles  Darwin,who 
worked  out  the  fertilization  of  this  flower,  describes  it  as  follows  : 
"  When  })ees  suck  the  flowers,  the  anthers  of  the  longest  stamens  .  .  . 
are  rubbed  against  the  abdomen  and  inner  sides  of  the  hind  legs 
as  is  likewise  the  stigma  of  the  long-styled  form  (see  diagram). 
The  anthers  of  the  midlength  stamens  and  the  stigma  of  the 
midstyled  form  are  rubbed  against  the  upper  side  of  the  thorax 
and  between  the  front  pair  of  legs.  And,  lastly,  the  anther  of 
the  shortest  stamens  and  the  stigma  of  the  short-styled  form  are 
rubbed  against  the  proboscis  and  the  chin;  for  the  bees  in  suck- 
ing the  flowers  insert  only  the  front  part  of  the  head  into  the 
flower.  ...  It  follows  that  insects  will  generally  carry  the  pollen 
of  each  form  from  the  stamens  to  the  pistil  of  corresponding 
length."  1 

Protection  of  Pollen.  —  Pollen,  in  order  to  be  carried  effectively 
by  the  wind,  insects,  or  other  agencies,  must  be  dry.  In  some 
flowers  the  irregular  form  of  the  corolla  protects  the  pollen  from 
dampness.  Other  flowers  close  up  at  night,  as  the  morning-glory 
and  four-o'clock.  Still  others,  as  the  bellflower,  droop  during  a 
shower  or  at  night. 

Pollen  is  also  protected  from  insect  visitors  which  would  carry 

»  Forma  of  Flowers,  page  169. 
HUNT.    E8.    BIO. 4 


50  FLOWERS  AND  THEIR  WORK 

off  pollen  but  give  the  flower  no  return  by  cross-pollinating  it. 
In  some  flowers  access  of  ants,  plant  lice,  or  other  small  crawling 
insects  to  the  stamens  is  rendered  difficult  by  hairs  which  are 
developed  upon  the  filaments  or  on  the  corolla.  Sometimes  a 
ring  of  sticky  material  is  found  making  a  barrier  around  the 
stalk  underneath  the  flower.  Many  other  adaptations  of  this 
sort  might  be  mentioned. 

Artificial  Cross-Pollination  and  its  Practical  Benefits  to  Man.  — - 
Artificial  cross-pollination  is  practiced  by  plant  breeders  and  can 
easily  be  tried  in  the  laboratory  or  at  home.  First  the  anthers 
must  be  carefully  removed  from  the  bud  of  the  flower  so  as  to  elim- 
inate all  possibility  of  self-pollination.  The  flower  must  then  be 
covered  so  as  to  prevent  access  of  pollen  from  without ;  when  the 
ovary  is  sufficiently  developed,  pollen  from  another  flower,  having 
the  characters  desired,  is  placed  on  the  stigma  and  the  flower 
again  covered  to  prevent  any  other  pollen  reaching  the  flower. 

The  seeds  from  this  flower  when  planted  may  give  rise  to  plants 
with  some  characters  like  each  of  the  plants  from  which  the  pollen 
and  egg  cell  came.  Artificial  fertilization  has  been  made  of  great 
practical  value  to  man. 

Rkference  Books 

elementary 

Sharpe,  A  Laboratory  Manual  for  the  Solution  of  Problems  in  Biology.  American  Book 

Company. 
Andrews,  Botany  all  the  Year  Round,  pages  222-236.     American  Book  Company. 
Atkinson,  First  Studies  of  Plant  Life,  Chaps.  XXV-XXVI.     Ginn  and  Company, 
Bailey,  Lessons  with  Plants,  Part  III,  pages  131-250.     The  Macmillan  Company. 
Coulter,  Plant  Studies,  Chap.  VII.     D.  Appleton  and  Company. 
Dana,  Plants  and  their  Children,  pages  187-255.     American  Book  Company. 
Lubbock,  Flowers,  Fruits,  and  Leaves,  Part  I.     The  Macmillan  Company. 
Newell,  A  Reader  in  Botany,  Part  II,  pages  1-96.     Ginn  and  Company. 

ADVANCED 

Bailey,  Plant  Breeding.     The  Macmillan  Company. 

Campbell.  Lectures  on  the  Evolution  of  Plants.    The  Macmillan  Company. 
Coulter,  Barnes,  and  Cowles,  A  Textbook  of  Botany,  Part  II.    American  Book  Com- 
pany. 
Darwin,  Different  Forms  of  Flowers  on  Plants  of  the  Same  Species.    D.  Appleton  &  Co. 
Darwin,  Fertilization  in  the  Vegetable  Kingdom,  Chaps.  I  and  II.    D.  Appleton  &  Co. 
Darwin,  Orchids  Fertilized  by  Insects.     D.  Appleton  and  Company. 
Gray,  Structural  Botany.    American  Book  Company. 
Lubbock,  British  Wild  Flowers.    The  Macmillan  Company. 
Miiller,  The  Fertilization  of  Flowers.    The  Macmillan  Company. 


V.   FRUITS  AND  THEIR  USES 

Problem  VTIT.    A  study  of  fruits  to  discover  — 

{a)  Tlielr  uses  to  a  plant. 

(J))  The  means  of  scattering. 

(c)  TJieir  prote<^tion  from  animals  and  other  enemies. 
{Laboratory  Manual,  Prob.  VIII.) 

A  Typical  Fruit,  —  the  Pea  or  Bean  Pod.  —  If  a  withered  flower 
of  any  one  of  the  pea  or  bean  family  is  examined  carefully,  it  will 
be  found  that  the  pistil  of  the  flower  continues  to  grow  after  the 
rest  of  the  flower  withers.  If  we  remove  the  pistil  from  such  a 
flower  and  examine  it  carefully,  we  find  that  it  is  the  ovary  that 
has  enlarged.  The  space  within  the  ovary  has  become  almost  filled 
with  a  number  of  al- 
most ovoid  bodies,  at- 
tached along  one  edge 
of  the  inner  wall. 
These  we  recognize  as 
the  young  seeds. 

The    Dod    of   a    bean       ^^^^  of  the   black  locust;   a  legume,  showing  the 
'  attachment  of  the  seeds. 

pea,  or  locust  illustrates 

well  the  growth  from  the  flower.  The  flower  stalk,  the  ovary,  and 
the  remains  of  the  style,  the  stigma,  and  the  calyx,  can  be  found 
on  most  unopened  pods.  If  the  pod  is  opened,  the  seeds  will  be 
found  fastened  to  the  ovary  wall  each  by  a  little  stalk.  That 
part  of  the  ovary  wall  which  bears  the  seeds  is  the  placenta. 
The  walls  of  the  pod  are  called  valves. 

The  pod,  which  is  in  reality  a  ripened  ovary  with  other  parts  of 
the  pistil  attached  to  it,  is  considered  as  a  fruit.  By  definition, 
a  fruit  is  a  ripened  ovary  together  with  any  parts  of  the  flower  that  may 
be  attached  to  it.  The  chief  use  of  the  fruit  to  the  flower  is  to  hold 
and  to  protect  the  seeds ;  it  may  ultimately  distribute  them  where 
they  can  reproduce  young  plants. 

51 


52  FRUITS  AND   THEIR  USES 

Formation  of  Seeds.  —  Each  seed  has  been  formed  as  a  direct 
result  of  the  fertilization  of  the  egg  cell  {contained  in  the  embryo  sac 
of  the  ovule)  by  a  sperm  cell  of  the  pollen  tube. 

Seed  Dispersal.^  —  If  you  will  go  out  any  fall  afternoon  into 
the  fields,  a  city  park,  or  even  a  vacant  lot,  you  can  hardly  es- 
cape seeing  how  seeds  are  scattered  by  the  parent  plants  and  trees. 
Several  hundred  little  seedling  trees  may  often  be  counted 
under  the  shade  of  a  single  maple  or  oak  tree.  But  nearly  all 
these  young  trees  are  doomed  to  die,  because  of  the  overshading 
and  crowding.      Plants,  like  animals,  are  dependent  upon  their 


Young  cedars  around  parent  tree.     Photographed  by  Overton. 

surroundings  for  food  and  air.  They  need  light  even  more  than 
animals  need  it,  because  the  soil  directly  under  the  shade  of  the 
old  tree  gives  only  raw  food  material  to  the  plants,  and  they  must 
have  sunlight  in  order  to  make  food.  This  overcrowding  is  seen 
in  the  garden  where  young  beets  or  lettuce  are  growing.  The 
gardener  assists  nature  by  thinning  out  the  young  plants  so  that 
they  may  not  be  handicapped  in  their  battle  for  life  in  the 
garden  by  an  insufficient  supply  of  air,  light,  and  food. 

1  At  this  point  a  field  trip  may  well  be  taken  with  a  view  to  finding  out  how 
the  common  fall  weeds  scatter  their  seeds.  Fruits  and  seeds  obtained  upon  this 
trip  will  make  a  basis  for  laboratory  work  on  the  adaptations  of  seed  and  fruit  for 
dispersal. 


FRUITS  AND   THEIR   USES 


53 


The  blackberry,  a  fruit  having  small  seeds 
scattered  by  birds. 


It  is  evidently  of  considerable  advantage  to  a  plant  to  be  able 
to  place  its  progeny,  which  are  to  grow  up  from  seeds,  at  a  consider- 
able distance  from  itself,  in  order  that  the  young  plant  may  })e  pro- 
vided with  a  sufficient  space  to  get  nourishment  and  foothold.  This 
is  the  result  which  plants  have 
to  accom])lish.  Some  accom- 
plish the  result  more  com- 
pletely than  others,  and  thus 
are  the  more  successful  ones 
in  the  battle  of  life. 

Adaptations  for  Seed  Disper- 
sal; Fleshy  Fruits  with  Hard 
Seeds.- — Plants  are  fitted  to 
scatter  their  seeds  by  having 
the  special  means  either  in  the 
fruit  or  in  the  seed.  Various 
agents,  as  the  wind,  water,  or 
squirrels,  birds,  and  other  animals,  make  it  possible  for  the  seeds 
to  be  taken  away  from  the  plant. 

Fleshy  fruits,  that  is,  such  fruits  as  contain  considerable  water 
when  ripe,  are  eaten  by  animals  and  the  seeds  passed  off  undigested. 
Most  wild  fleshy  fruits  have  small,  hard,  indigestible  seeds.  Birds 
are  responsible  for  much  seed  planting  of  berries  or  other  small  fruit. 
Bears  and  other  berry-feeding  animals  aid  in  this  as  well.  Some 
seeds  have  especial  adaptations  in  the  way  of  spines  or  projections. 
Insects  make  use  of  these  projections  in  order  to  carry  them  away. 
Ants  plant  seeds  which  they  have  carried  to  their  nests  for  a  food 
supply.     Nuts  are  planted  by  squirrels  and  blue  jays. 

Suggestions  for  Field  Work.  —  Examine  the  fruit  of  huckleberry,  black- 
berry, wild  strawberry,  wild  cherry,  black  haw,  wild  grape,  tomato, 
currant.  Report  how  many  of  the  above  have  seeds  with  hard  coatings. 
Notice  that  in  most,  if  not  in  all,  edible  fruits,  the  fruit  remains  green, 
sour,  and  inedible  until  the  seeds  are  ripe.  In  the  state  of  nature,  how 
might  this  be  of  use  to  a  plant  ? 

Hooks  and  Spines.  —  Some  fruits  which  are  dry  and  have  a  hard 
external  covering  when  ripe  possess  hooks  or  spines  which  enable 
the  whole  fruit  to  be  carried  away  from  the  parent  plant  by  animals 
or  other  moving  objects.     Cattle  are  responsible  for  the  spread  of 


54 


FRUITS  AND  THEIR  USES 


The  cocklebur.    Note  the  curved 
hooks. 


some  of  our  worst  weeds  in  this  way.     The  burdock  and  clotbur  are 
famiHar  examples.     In  both  the  mass  of  Uttle  hooks  is  all  that  re- 
mains of  an  involucre.     Thus  the  whole 
fruit  cluster  may  be  carried  about  and 
j^iiriife     ^^Sl^      seeds  scattered.     In  many  of  the  Com- 
-^SHHRP'     ^^S^      posites,  as  in  the  cockleburs  and  beg- 
^T^TlffT^  ~^^^        gar's-ticks,  the  fruits  are  provided  with 

strong  curved   projections  which   bear 
many  smaller  hooklike  barbs. 

Pappus.  —  Probably  the  most  im- 
portant adaptations  for  dispersal  of  seeds  are  those  by  which  the 
fruit  is  fitted  for  dispersal  by  the  wind.  That  much-loved  and 
much-hated  weed,  the  dandelion,  gives  us  an  example  of  a  plant  in 
which  the  whole  fruit  is  carried  by  the  wind.  The  parachute,  or 
pappus,  is  an  outgrowth  of  the  ovary  wall.  Many  other  fruits, 
notably  that  of  the 
Canada  thistle,  are 
provided  with  the  pap- 
pus as  a  means  of 
getting  away.  In  the 
milkweed  the  seeds 
have  developed  a  silky 
outgrowth  which  may 
carry  them  for  miles. 
In  New  York  city  the 
air  is  sometimes  full  of 
the  dowh  from  these 
seeds,  which  is  brought 
from  far  over  the 
meadows  of  New  Jer- 
sey by  the  prevailing 
westerly  wind. 

Dehiscent  Fruits  and 
how  they  Scatter  Seeds. 
—  One  of  the  many  meth- 
ods of  getting  rid  of  seeds 

is  seen  in  dry  fruits.     These  simply  split  to  allow  of  the  escape  of  the 
Examples  of  common  fruits  that  split  open  (dehiscent)  are  seen 


Dandelion  heads ;  the  middle  one  a  mass  of  ripe 
fruits  ready  to  be  scattered  by  the  wind.  Photo- 
graphed by  Overton. 


FRUITS  AND   THEIR  USES 


55 


in  the  follicle  of  the  milkweed,  a  fruit  which  splits  along  the  edge  of  one 
valve,  the  pod  or  legume  of  a  pea  and  the  bean,  and  the  capsule  of 
Jimson  weed  and  the  evening  primrose.  In  all  of  the  above,  the  ovary 
wall  does  not  split  open  until  the  seeds  are  fully  ripe. 
This  helps  to  insure  the  future  growth  of  the  seed. 
Some  dehiscent  fruits  scatter  their  seeds  through  the 
explosion  of  the  seed  case.  Such  a  fruit  is  the  witch- 
hazel,  which  explodes  with  such  force  that  the  seeds  are 
thrown  several  feet.  The  wild  geranium,  a  five-loculed 
capsule,  splits  along  the  edge  of  each  locule,  snaps  back, 
and  throws  the  seed  for  some  distance.  Jewelweed 
fruits  burst  open  in  somewhat  the  same  manner. 


Capsule  of  crane's- 
bill  discharging 
its  seed. 


Winged    Seeds.  —  The  seeds  of  the  pine,  held 
underneath  the  scales  of  the  cone,  are  prolonged 
into  wings,  which  aid  in  their  dispersal.     The  seeds  of  many  of 
our  trees  are  thus  scattered. 

Other  Methods.  —  Sometimes  whole  plants  are  carried  by  the 
high  winds  of  the  fall.  This  is  effected  in  the  plants  called  tumble- 
weeds,  in  which  the  plant  body,  as  it  dries,  assumes  a  somewhat 
spherical  shape.     The  main  stalk  breaks  off,  and  the  plant  may 

then  be  blown  along  the  ground, 
scattering  seeds  as  it  goes,  until 
it  is  ultimately  stopped  by  a 
fence  or  bush.  A  single  plant 
of  Russian  thistle  may  thus 
scatter  over  two  hundred  thou- 
sand seeds. 

Seeds  or  fruits  (for  example, 
the  coconut)  may  fall  into  the 
water  and  be  carried  thousands 
of  miles  to  their  new  resting 
place,  the  fibrous  husk  provid- 
ing a  boat  in  which  the  seed 
is  carried. 

Other  seeds  may  collect  in 
the  mud  along  the  banks  of 
ponds  or  streams.  Birds  which  come  there  to  feed  upon  these  and 
other  material  in  the  mud  may  carry  many  seeds  in  the  mud 
attached  to  their  feet.     The   great   English   naturalist,   Charles 


Cross  section  of  a  coconut  in  its  fibrous 
husk. 


56 


FRUITS   AND   THEIR  USES 


Darwin,  raised  eighty-two  plants  from  seeds  thus  carried  by  a 
bird.  It  is  probable  that  by  means  of  birds  and  water  most  of 
the  vegetation  has  come  into  existence  on  the  newly  formed  coral 
islands  of  the  Pacific  Ocean. 

Some  Other  Forms  of  Fruits  and  their  Method  of  Dispersal.  —  Dry 

fruits  which  do  not  split  open  to  allow  of  the  escape  of  their  seeds  are 
known  as  indehiscent  fruits.  Some  are  known  as 
grains.  Such  are  corn,  wheat,  oats,  etc.  A  grain 
is  simply  a  one-seeded  fruit  in  which  the  wall  of 
the  ovary  has  grown  so  closely  to  that  of  the  seed 
that  they  cannot  be  separated.  Such  fruits  are 
usually  small  and  numerous,  having  a  thin  outer 
wall.  The  seed  may  easily  germinate  under  favor- 
able conditions.  Other  indehiscent  fruits  are  nuts, 
one-seeded  fruits  with  usually  hard  outer  covering, 
the  so-called  key  fruits  of  the  maples  or  ash,  and 
many  others.  Some  indehiscent  fruits  are  light 
and  carried  by  the  wind ;  others  are  extremely 
numerous  and  may  be  scattered  by  animals.  The 
key  fruits  depend  upon  the  wind,  while  nuts  are 
often  carried  away,  buried,  and  forgotten  by  blue 
jays  and  squirrels,  and  thus  obtain  a  new  foothold. 

Large  Numbers 
of  Seeds.  —  Plants 
which  do  not  have 
especial  means  for 
scattering  their  seeds  may  make  up  for  this 
by  producing  a  large  number  of  seeds  and 
holding  them  in  podlike  fruits  which  are 
easily  shaken  by  the  wind.  The  Jimson 
weed  is  a  familiar  example  of  such  a  plant. 
Each  capsule  of  Jimson  weed  contains  from  four  hundred  to  six  hundred 
seeds,  depending  upon  its  size.     If  all  of  these  seeds  develop,  the  whole 

earth  would  soon  be  covered  with 
Jimson  weed,  to  the  exclusion  of 
all  other  forms  of  plant  life. 
That  this  is  not  the  case  is  due 
to  the  fact  that  only  those  seeds 
which  are  advantageously  placed 
can  develop ;  the  others  will,  for 
various  reasons  (lack  of  moisture 
to  start  the  young  seed  on  its 
way,  poor  soil,  lack  of  air  or  sunlight,  overcrowding),  fail  to  germi- 
uatQ. 


Grain;    spikes   of 
ened  flowers. 


rip- 


Key  fruit  of  maple. 


The  acorn,  a  nut  in  which  the  involucre 
partly  covers  the  fruit. 


FRUITS  AND   THEIR  USES  67 

The  Struggle  for  Existence.  —  Those  plants  which  provide  best 
for  their  young  are  usually  the  most  successful  in  life's  race.  Plants 
which  combine  with  the  ability  to  scatter  many  seeds  over  a  wide 
territory  the  additional  characteristics  of  rapid  growth,  resistance 
to  dangers  of  extreme  cold  or  heat,  attacks  of  parasitic  enemies, 
inedibility,  and  peculiar  adaptations  to  cross-pollination  or  self- 
pollination,  are  usually  spoken  of  as  weeds.  They  flourish  in  the 
sterile  soil  of  the  roadside  and  in  the  fertile  soil  of  the  garden.  By 
means  of  rapid  growth  they  kill  other  plants  of  slower  growth  by 
usurping  their  territory.  Slow-growing  plants  are  thus  actually 
exterminated.  Many  of  our  common  weeds  have  been  introduced 
from  other  countries  and  have,  through  their  numerous  adaptations, 
driven  out  other  plants  which  stood  in  their  way.  Such  is  the  Rus- 
sian thistle.  P^irst  introduced  from  Russia  in  1873,  it  spread  so 
rapidly  that  in  twenty  years  it  had  appeared  as  a  common  weed 
over  an  area  of  some  twenty-five  thousand  square  miles.  It  is 
now  one  of  the  greatest  pests  in  our  Northwest. 

Problem  IX.  The  economic  value  of  some  fruits,  {Labor a- 
tory  Manual,  Prob.  IX.) 

Economic  Value  of  Fruits.  —  Our  grains  are  the  cultivated  prog- 
eny of  wild  grasses.  Domestication  of  plants  and  animals  marks 
epochs  in  the  advance  of  civihzation.  The  man  of  the  stone  age 
hunted  wild  beasts  for  food,  and  lived  like  one  of  them  in  a  cave  or 
wherever  he  happened  to  be;  he  was  a  nomad,  a  wanderer,  with 
no  fixed  home.  He  may  have  discovered  that  wild  roots  or  grains 
were  good  to  eat ;  perhaps  he  stored  some  away  for  future  use. 
Then  came  the  idea  of  growing  things  at  home  instead  of  digging  or 
gathering  the  wild  fruits  from  the  forest  and  plain.  The  tribes 
which  first  cultivated  the  soil  made  a  great  step  in  advance,  for  they 
had  as  a  result  a  fixed  place  for  habitation.  The  cultivation  of 
grains  and  cereals  gave  them  a  store  of  food  which  could  be  used 
at  times  when  other  food  was  scarce.  The  word  "cereal"  (derived 
from  Ceres,  the  Roman  Goddess  of  Agriculture)  shows  the  impor- 
tance of  this  crop  to  Roman  civilization.  From  earliest  times  the 
growing  of  grain  and  the  progress  of  civilization  have  gone 
hand  in  hand.  As  nations  have  advanced  in  power,  their 
dependence  upon  the  cereal  crops  has  been  greater  and  greater. 


58 


FRUITS  AND   THEIR   USES 


'*  Indian  corn,"  says  John  Fiske,  in  The  Discovery  of  America, 
"  has  played  a  most  important  part  in  the  discovery  of  the  New 
World.  It  could  be  planted  without  clearing  or  plowing  the  soil. 
There  was  no  need  of  threshing  or  winnowing.  Sown  in  tilled  land, 
it  yields  more  than  twice  as  much  food  per  acre  as  any  other  kind 
of  grain.  This  was  of  incalculable  advantage  to  the  English  settlers 
in  New  England,  who  would  have  found  it  much  harder  to  gain  a 
secure  foothold  upon  the  soil  if  they  had  had  to  begin  by  preparing 
it  for  wheat  or  rye." 


i-,_U  ^ 


CORN  „^   ^ 

^Stf^<7  to  SZOO.bushels  per  scjuare  mile     "  \ 

^^  oyer  3200       ... 


-J 


Indian  Corn  Production— Percentage 

30  40  50  60  70 

m--     I        I     ^ — 'I     II 


MP 


Jllincds 


Lowa 


Neb.        Mo.      Kan.  Ohio  Ind.  Tex.        Rest  of  United  States 


To-day,  in  spite  of  the  great  wealth  which  comes  from  our  mineral 
resources,  live  stock,  and  manufactured  products,  the  surest  index 
of  our  country's  prosperity  is  the  size  of  the  wheat  and  corn  crop. 
According  to  the  last  census,  the  amount  of  capital  invested  in 
agriculture  was  over  $20,000,000,000,  while  that  invested  in  man- 
ufacture was  less  than  one  half  that  amount. 

Corn.  —  About  three  billion  bushels  of  corn  were  raised  in  the 
United  States  during  the  year  1910.  This  figure  is  so  enormous 
that  it  has  but  little  meaning  to  us.     In  the  past  half  century 


FRUITS  AND  THEIR  USES 


59 


our  corn  crop  has  increased  over  350  per  cent.  Illinois  and  Iowa 
are  the  greatest  corn-producing  states,  each  having  a  yearly  record 
of  over  four  hundred  million  bushels.  The  Figure  on  page  58 
shows  the  principal  corn-producing  areas  in  the  United  States. 

Indian  corn  is  put  to  many  uses.  It  is  a  valuable  food.  It  con- 
tains a  large  proportion  of  starch,  from  which  glucose  and  alcohol 
are  made.  Machine  oil  and  soap  are  made  from  it.  The  leaves 
and  stalk  are  an  excellent  fodder ;  they  can  be  made  into  paper  and 
packing  material.  Mattresses  can  be  stuffed  with  the  husks.  The 
pith  is  used  as  a  protective  belt  placed  below  the  water  line  of  our 
huge  battleships.  Corn  cobs  are  used  for  fuel,  one  hundred  bushels 
having  the  fuel  value  of  a  ton  of  coal. 

Wheat.  —  Wheat  is  the  cro])  of  next  greatest  importance  in  size, 
and  is  of  even  greater  money  value  to  this  country.     Nearly  seven 


Wheat  Crop  in  United  States— Percentage  Source 

It 


TW^t 


I      '     »     t 


Minnesota     Kansas  N.Dak.  S.Dak.  Neb.    O.  Cal.Ind.Mo.Pa. 


Other  Sutes 


hundred  millions  of  bushels  were  raised  in  this  country  in  1910, 
representing  a  total  money  value  of  over  $700,000,000.  Seventy- 
two  per  cent  of  all  the  wheat  raised  comes  from  the  North  Central 
States  and  CaUfornia.     About  three  fourths  of  the  wheat  crop  is 


60  FRUITS  AND  THEIR  USES 

exported,  nearly  one  half  of  it  to  Great  Britain.  Wheat  has  its 
chief  use  in  its  manufacture  into  flour.  The  germ,  or  young  wheat 
plant,  is  sifted  out  during  this  process  and  made  into  breakfast  foods. 
Flour-making  forms  the  chief  industry  of  Minneapolis,  Minnesota, 
and  of  several  other  large  and  wealthy  cities  in  this  country. 

Other  Grains.  —  Of  the  other  grain  and  cereals  raised  in  this 
country,  oats  are  the  most  important  crop,  over  one  billion 
bushels  having  been  produced  in  1910.  lUinois,  Wisconsin,  Minne- 
sota, and  Iowa  produce  together  over  50  per  cent  of  the  total  yield. 
Oats  are  distinctly  a  Northern  crop,  over  95  per  cent  being  grown 
north  of  the  thirty-sixth  parallel.  Barley  is  another  largely 
Northern  crop;  a  staple  of  some  of  the  northern  countries  of 
Europe  and  Asia,  although  such  a  hardy  cereal.  Almost  three 
fourths  of  the  total  production  in  the  United  States  comes  from 
California,  Minnesota,  Wisconsin,  Iowa;  the  production  of  these 
states  may  be  roughly  estimated  as  86,000,000  bushels.  In  this 
country,  it  is  largely  used  for  making  malt  in  the  manufacture 
of  beer. 

Rye  is  the  most  important  cereal  crop  of  northern  Europe,  Russia, 
Germany,  and  Austro-Hungary  producing  over  50  per  cent  of  the 
world's  supply.  It  makes  the  principal  food  for  probably  one 
third  the  people  of  Europe,  being  made  into  "  black  bread."  It  is 
of  relatively  less  importance  as  a  crop  now  in  the  United  States 
than  in  former  years. 

Perhaps  one  of  the  most  important  grain  crops  for  the  world 
(although  relatively  unimportant  in  the  United  States)  is  rice. 
A  grassUke  plant,  its  fruit,  after  thrashing,  screening,  and  milling, 
forms  the  principal  food  of  one  third  of  the  human  race.  More- 
over, its  stems  furnish  straw,  its  husks  make  a  bran  used  as  food 
for  cattle,  and  the  grain,  when  distilled,  is  rich  in  alcohol. 

Nearly  related  to  the  grains  are  our  grasses.  There  is  a  total 
forage  crop  (exclusive  of  corn  stalks)  of  nearly  100,000,000  tons, 
valued  at  over  $600,000,000.  The  best  hay  in  the  eastern  part  of 
the  United  States  comes  from  dry  timothy  grass  and  clover,  the 
stems  and  leaves  as  well  as  the  fruits  forming  the  so-called  hay. 
In  some  parts  of  the  West  a  kind  of  clover  called  alfalfa  is  much 
grown,  it  being  adapted  to  the  semiarid  conditions  of  that  part  of 
the  country. 


FRUITS  AND   THEIR   USES 


61 


Cotton.  —  Among  our  fruits  cotton  is  probably  that  of  the  most 
importance  to  the  outside  world.  Over  eleven  million  bales  of  five 
hundred  pounds  each  are  raised  annually.  Of  this  amount  a  large 
amount  is  exported,  the  United  States  producing  over  three  fourths 
of  the  world's  cotton  supply.  The  relation  of  source  and  distribu- 
tion of  the  cotton  crop  can  be  seen  by  a  glance  at  the  accompany- 
ing diagram. 


COTTON 

^  I  to  20  bales  ^era<fuare  mile 
^AorerZO   .... 


Cotton  Crop  in  United  States— Percentage  Source 

iO  30  40  50  60  7,0  RO 


mmL 


Texas 


Georgia 


Miss. 


Alabama    S.Car.    Ark.      La.    N.C\Other  SUtes 


Percentage  Consumption— United  States  Cotton  Crop 

<P Bg 6,0  7,0  80 


United  States 
North  South 


Great  Britain  &  Ireland 


Germany       France  It.  Rst.Wld. 


The  cotton  plant  is  essentially  a  warmth-loving  plant.  Its 
commercial  importance  is  gained  because  the  seeds  of  the  fruit 
have  long  filaments  attached  to  them.  Bunches  of  these  filaments, 
after  treatment,  are  easily  twisted  into  threads  from  which  are 
manufactured  cotton  cloth,  muslin,  calico,  and  cambric.  In  addition 
to  the  fiber,  cottonseed  oil,  a  substitute  for  olive  oil,  is  made  from 
the  seeds,  and  the  refuse  remaining  makes  an  excellent  cattle  fodder. 


62 


FRUITS   AND   THEIR  USES 


Cotton  Boll  Weevil.  —  The  cotton  crop  of  the  United  States  has 
rather  recently  been  threatened  with  des.truction  by  a  beetle  called 
the  cotton  boll  weevil.  This  insect,  which  bores  into  the  young  pod 
of  the  cotton,  develops  there,  stunting  the  growth  of  the  fruit  to 
such  an  extent  seeds  are  not  produced.     The  loss  in  Texas  alone  is 


Map  showing  spread  of  the  cotton  boll  weevil.      It  was  introduced  from  Mexico 
about  1894.    What  proportion  of  the  cotton-raising  belt  was  infected  in  1908  ? 


estimated  at  over  $10,000,000  a  year.  The  boll  weevil,  because 
of  the  protection  offered  by  the  cotton  boll,  is  very  difficult  to  ex- 
terminate. The  weevils  are  destroyed  by  birds,  the  infected  bolls 
and  stalks  are  burnt,  miUions  are  killed  each  winter  by  cold,  other 
insects  prey  on  them,  but  at  the  present  time  they  are  one  of  the 
greatest  pests  the  South  knows  and  no  sure  method  of  extermina- 
tion has  been  found. 


FRUITS  AND   THEIR   USES 


63 


Cros8  section  of  a  cucumber,  a 
pepo.  Note  the  number  of 
locules  or  spaces  in  the  ovaiy. 
How  and  where  are  the  seeds 
attached  ? 


Garden  Fruits.  —  Green  plants  and  especially  vegetables   have 

come  to  play  an  important  part  in  the  dietary  of  man.     The  dis- 
eases known  as  scurvy  and  beri-beri, 

the  latter  the  curse  of  the  far  Eastern 

na\'ies,  have  been  largely  prevented  by 

adding  vegetables  and  fruit  juices  to 

the  dietar}^  of  the  sailors.     People  in 

this  country  are  beginning  to  find  that 

more    vegetables   and    less  meat   are 

better  than  the  meat  diet  so  often  used. 

Market  gardening  forms  the  lucrative 

business  of  many  thousands  of  people 

near  our  great  cities.     Some  of  the 

most  important  fleshy  fruits — squash, 

cucumbers,  pumpkins,  and  melons  — 

are  examples  of  the  pepo  type  of  fruit ;  tomatoes  and  peppers  are 

types  of  henries  in  botanical  language  (for  a  berry  is  any  soft 

or  juicy  fruit  containing  small  seeds). 
The  berries — strawberries,  raspberries, 
and  blackberries — of  our  gardens  bring 
in  an  annual  income  of  $26,000,000  to 
our  fruit  raisers.  Beans  and  peas  are 
important  as  foods  because  of  their 
relatively  large  amount  of  proteid. 
Peanuts,  rather  curiously,  are  true  leg- 
umes, like  peas  and  beans,  but  develop 
underground.  Canning  green  corn, 
peas,  beans,  and  tomatoes  has  become  an 
important  business. 

Orchard  and  Other 
Fruits. — In  the  United 

States  over  one  hundred  and  seventy-five  milhon 

bushels  of  apples  are  grown  every  year.      Pears, 

plums,  apricots,  peaches,  and  nectarines  also  form 

large   orchards,    especially  in  California.     Nuts  The   blackberry,    a 

form  one  of  our  important  articles  of  food,  largely      ^^'^  "^^^^  "^"^ .  °^ 

,  e    ^       ^  J        o    J        many  separate  npe 

because  of  the  large  amount  of  proteid  contained     carpels, 
in  them. 


Cross  section  of  a  green  pepper, 
a  berry.  How  many  locules 
has  the  ovary?  Note  the 
arrangement  of  the  seeds. 


64  FRUITS  AND  THEIR  USES 

The  grape  crop  of  the  world  is  commercially  valuable,  because  of 
the  raisins  and  wine  produced.  Lemons,  oranges,  and  grapefruit 
have  come  in  recent  years  to  give  a  living  to  many  people  in  this 
country  as  well  as  in  other  parts  of  the  world.  The  unfortunate  city 
of  Messina  was  the  center  of  the  lemon  industry  for  Italy.  Figs, 
olives,  and  dates  are  staple  foods  in  the  Mediterranean  countries 
and  are  sources  of  wealth  to  the  people  there,  as  are  coconuts, 
bananas,  and  many  other  fruits  in  tropical  countries. 

Beverages  and  Condiments.  —  The  coffee  and  cocoa  beans, 
both  products  of  tropical  regions,  form  the  basis  of  two  very 
important  beverages  of  civilized  man.  Pepper,  black  and  red, 
mustard,  allspice,  nutmegs,  cloves,  and  vanilla  are  all  products 
manufactured  from  various  fruits  or  seeds  of  tropical  plants. 

Reference  Books 

elementary 

Sharpe,  A  Laboratory  Manual  for  the  Solution  of  Problems  in  Biology.     American 

Book  Company. 
Atkinson,  First  Studies  of  Plant  Life,  Chap.  XXIII.     Ginn  and  Company. 
Bailey,  Botany,  Chaps.  XXI,  XXII.     The  Macmillan  Company. 
Bailey,  Lessons  with  Plants,  pages  251-314.     The  Macmillan  Company. 
Beal,  Seed  Dispersal.     Ginn  and  Company. 

Bergen  and  Davis,  Principles  of  Botany,  Chaps.  XL,  XLI.     Ginn  and  Company. 
Coulter,  Plant  Studies,  Chap.  VI.     D.  Appleton  and  Company. 
Dana,  Plants  and  their  Children,  pages  27-49.     American  Book  Company. 
Gannett,  Garrison,  and  Houston,  Commercial  Geography.    American  Book  Company. 
Goff  and  Mayne,  First  Principles  of  Agriculture.     American  Book  Company. 
Lubbock,  Flowers,  Fruits,  and  Leaves.     The  Macmillan  Company. 
Newell,  Reader  in  Botany,  pages  97-137.     Ginn  and  Company. 

ADVANCED 

Bailey,  The  Evolution  of  our  Native  Fruits.     The  Macmillan  Company. 
Bailey,  Plant  Breeding.    The  Macmillan  Company. 

Coulter,  Barnes,  and  Cowles,  A  Textbook  of  Botany,  Vol.  I.    American  Book  Com- 
pany. 
De  CandoUe,  Origin  of  Cultivated  Plants.     D.  Appleton  and  Company. 
Farmers'  Bulletins,  Nos.  78,  86,  225,  344.     U.S.  Department  of  Agriculture. 
Hodge,  Nature  Study  and  Life,  Chaps.  X,  XI.     Ginn  and  Company. 
Kerner  (translated  by  Oliver),  Natural  History  of  Plants.     Henry  Holt  and  Com- 
pany.    4  vols.     Vol.  II,  Part  2. 
Sargent,  Com  Plants.     Houghton,  Mifflin,  and  Company. 


VI.  SEEDS  AND  SEEDLINGS 


Prohlem  X.  A  study  of  seeds  in  tJieir  relation  to  the  new 
plant.    {Laboratory  Manual ,  Frdb.  X.) 

(a)    The  relation  of  the  young  plant  to  its  food  supply. 
(Jb)    How  the  young  plant  makes  use  of  its  food  supply. 

Relation  of  Flower  to  Fruit.  —  We  have  already  found  in  our 
study  of  the  fruit  that  the  bean  pod  is  a  direct  outgrowth  from  the 
flower.  It  iSy  in  fact,  the  ovary  of  the  flower,  with  the  parts  imme- 
diately surrounding  it,  which  has  grown  larger  to  make  a  fruit. 

Use  of  Fruit.  —  The  fruit  holds  and  protects  the  seeds  until  the 
time  comes  when  they  are  able  to  germinate  and  produce  new 
plants  like  the  original  plant 
from  which  they  grew.     Then, 
as  we  have  seen,  it  helps  to 
scatter  them  far  and  wide. 

The  Bean  Seed.  —  We  have 
already  been  able  to  identify  in 
the  pod  of  the  bean  the  style, 
stigma,  and  ovary  of  the  flower. 
The  opened  pod  discloses  tho 
seeds  lying  along  one  edge  of 
the  pod,  each  attached  by  a 
little  stalk  to  the  inner  wall  of 
the  ovary.  If  we  pull  a  single 
bean  from  its  attachment,  we 
find  that  the  stalk  leaves  a  scar 
on  the  coat  of  the  bean;  this 
scar  is  called  the  hilum.  The 
tiny  hole  near  the  hilum  is 
called    the    micropyle.     Turn 

back  to  the  Figure  (p.  37)  showing  the  ovule  in  the  ovary.  Find 
there  the  httle  hole  through  which  the  pollen  tube  reached  the 
embryo  sac.     This  hole  is  called  the  micropyle,  and  is  identical 

HUNT.  ES.  BIO. — 5  65 


Three  views  of  a  kidney  bean,  the  lower 
one  having  one  cotyledon  removed  to 
show  the  hyi)ocotyl  and  plumule. 


66  SEEDS  AND  SEEDLINGS 

with  the  micropyle  in  the  seed.  The  thick  outer  coat  (the  testa) 
is  easily  removed  from  a  soaked  bean,  the  dehcate  coat  under  it 
easily  escaping  notice.  The  seed  separates  into  two  parts ;  these  are 
called  the  cotyledons.  If  you  pull  apart  the  cotyledons  very  care- 
fully, you  find  certain  other  structures  between  them.  The  rod- 
like part  is  called  the  hypocotyl  (meaning  under  the  cotyledons). 
This  will  later  form  the  root  (and  part  of  the  stem)  of  the  young 
bean  plant.  The  first  true  leaves,  very  tiny  structures,  are  folded 
together  between  the  cotyledons.  That  part  of  the  plant  above 
the  cotyledons  is  known  as  the  plumule  or  epicotyl  (meaning  above 
the  cotyledons).  All  the  parts  of  the  seed  within  the  seed  coats 
together  form  the  embryo  or  young  plant.  A  bean  seed  contains, 
then,  a  tiny  plant  tucked  away  between  the  cotyledons  and  pro- 
tected by  a  tough  coat. 

Food  in  the  Cotyledons.  —  The  problem  now  before  us  is  to  find 
out  how  the  embryo  of  the  bean  is  adapted  to  grow  into  an  adult 
plant.  Up  to  this  stage  of  its  existence  it  has  had  the  advantage 
of  food  and  protection  from  the  parent  plant.  Now  it  must  begin 
the  battle  of  life  alone.  We  shall  find  in  all  our  work  with  plants 
and  animals  that  the  problem  of  food  supply  is  always  the  most 
important  problem  to  be  solved  by  the  growing  organism.  Let 
us  see  if  the  embryo  is  able  to  get  a  start  in  life  (which  many  ani- 
mals get  in  the  egg)  from  food  provided  for  it  within  its  own  body. 
Test  for  Starch.  —  If  we  shake  up  a  piece 
of  laundry  starch  in  water,  in  a  test  tube, 
and  then  add  to  the  mixture  two  or  three 
drops  of  iodine  solution,^  we  find  that  the 
particles  of  starch  in  the  test  tube  turn  pur- 
ple or  deep  blue.  It  has  been  discovered  by 
experiment  that  starch,  and  no  other  known 
„,     ^      .     .    .,.      „    substance,  will  be  turned  purple  or  dark  blue. 

Starch  grains  in  the  cells   r^^^         c  -     ^^  i      •         i 

of  a  potato  tuber.        Therefore,   lodme  solution  has  come   to   be 

used  as  a  test  for  the  presence  of  starch. 
Starch  in  the  Bean. — If  we  mash  up  a  little  piece  of  a  bean  cotyle- 

*  Iodine  solution  is  made  by  simply  adding  a  few  crystals  of  the  element  iodine 
to  95  per  cent  alcohol ;  or,  better,  take  by  weight  1  gram  of  iodine  crystals,  | 
gram  of  iodide  of  potassium,  and  dilute  to  a  dark  brown  color  in  weak  alcohol  (35 
per  cent)  or  distilled  water. 


SEEDS  AND  SEEDLINGS  67 

don  which  has  been  previously  soaked  in  water,  and  test  for  starch 
with  iodine  solution,  the  characteristic  blue-black  color  appears, 
showing  the  presence  of  the  starch.  If  a  little  of  the  stained  mate- 
rial is  mounted  in  water  on  a  glass  slide  under  the  compound  micro- 
scope, you  will  find  that  the  starch  is  contained  in  the  form  of  little 
ovoid  bodies  called  starch  grains.  The  starch  grains  and  other 
food  products  are  made  use  of  by  the  growing  plant. 

Starches  and  sugars  make  up  the  great  class  of  nutrients  known 
as  carbohydrates.  Of  these  we  shall  learn  more  when  we  take  up 
the  study  of  foods.  (The  teacher  may  here  refer  to  the  chapter 
on  Foods.) 

Proteid  in  the  Bean.  —  Another  nutrient  present  in  the  bean 
cotyledon  is  proteid.  Several  tests  are  used  to  detect  the  presence 
of  this  nutrient.     The  following  is  one  of  the  best  known:  — 

Place  in  a  test  tube  the  substance  to  be  tested ;  for  example,  a 
bit  of  hard-lx)iled  egg.  Pour  over  it  a  little  strong  (80  per  cent) 
nitric  acid.  Note  the  color  that  appears  —  a  lemon  yellow.  If 
the  egg  is  washed  in  water  and  a  little  ammonium  hydrate  added, 
the  color  changes  to  a  deep  orange,  showing  that  a  proteid  is 
present. 

If  the  proteid  is  in  a  liquid  state,  its  presence  may  be  proved 
by  heating,  for  when  it  coagulates  or  thickens,  as  does  the 
white  of  an  egg  when  boiled,  proteid  in  the  form  of  an  albumin 
is  present. 

Another  characteristic  proteid  test  easily  made  at  home  is 
burning  the  substance.  If  it  burns  with  the  odor  of  burning  feathers 
or  leather,  then  proteid  forms  part  of  its  composition. 

Proteids  occur  in  several  different  forms,  but  the  preceding  tests 
will  cover  most  cases  commonly  met.  White  of  egg,  lean  meat, 
beans,  and  peas  are  examples  of  substances  composed  in  a  large 
part  of  proteid. 

A  test  of  the  cotyledon  of  a  bean  for  proteid  food  with  nitric  acid 
and  ammonium  hydrate  shows  us  that  considerable  proteid  is 
present.  It  contains  not  less  than  23  per  cent  of  proteid,  57  per 
cent  of  carbohydrates,  and  about  2  per  cent  of  fats. 

The  above  tests  show  us  that  the  bean  seed  contains  a  large 
supply  of  food  which,  as  we  shall  see,  is  used  by  the  young  plant 
in  its  germination. 


68 


SEEDS  AND  SEEDLINGS 


Beans  and  Peas  as  Food  for  Man.  —  The  young  plant  within 
a  pea  or  bean  is  well  supplied  with  nourishment  until  it  is  able  to 
take  care  of  itself.  In  this  respect  it  is  somewhat  like  a  young 
animal  within  the  egg,  a  bird  or  fish,  for  example.  So  much 
food  is  stored  in  legumes  (as  beans  and  peas  are  named)  that 
man  has  come  to  consider  them  a  very  valuable  and  cheap  source 
of  food.  The  following  table  shows  the  amount  of  food  material 
that  can  be  purchased  for  10  cents  in  fresh  and  dried  peas  and 
beans. 

Nutrients  furnished  for  Ten  Cents  in  Beans  and  Peas  at  Cer- 
tain Prices  per  Pound 


Food  Materials  as  Purchased 


Prices 

PER 

Pound 


Ten  Cents  will  pay  por- 


Total 

Food 

Material 


Proteid 


Fat 


Carbo- 
hydrates 


Kidney  beans,  dried  .... 
Lima  beans,  fresh,  in  pod  .  . 
Lima  beans,  fresh,  shelled       .     . 

Lima  beans,  canned 

Lima  beans,  dried 

String  beans,  fresh,  30  cents  per 

peck 

Beans,  baked,  canned    .... 

Lentils,  dried 

Peas,  green,  in  pod,  30  cents  per 

peck 

Peas,  canned 

Peas,  dried 


Cents 

5 
4 
8 
6 
6 

3 

5 

10 

3 

7 
4 


Pounds 

2.00 
2.50 
1.25 
1.67 
1.67 

3.33 
2.00 
1.00 

3.33 
1.43 
2.50 


Pounds 

0.45 
.08 
.04 
.07 
.30 

.07 
.14 
.26 

.12 
.05 
.62 


Pounds 

0.04 
.01 

.01 
.03 

.01 
.05 
.01 

.01 

.03 


Pounds 

1.19 
.25 
.12 
.24 

1.10 

.23 
.39 
.59 

.33 

.14 
1.55 


The  Corn.  —  The  ear  of  corn  is  not  a  single  fruit,  but  a  large 
number  of  fruits  in  a  cluster  like  a  bunch  of  bananas,  for  example. 
The  husk  of  an  ear  of  corn  is  simply  a  covering  of  leaflike  parts 
which  has  grown  over  the  young  fruits  for  their  better  protection. 
The  corn  cob  is  the  much  thickened  flower  stalk  on  which  the 
flowers  were  clustered.  If  you  have  removed  the  husk  carefully, 
you  will  see  part  of  each  flower  remaining  attached  to  each  grain 
of  corn.  The  so-called  silk  of  corn  is  nothing  more  than  a  long 
style  and  stigma.     The  corn  grain  itself  was  also  part  of  the 


SEEDS  AND   SEEDLINGS 


flower  —  the  same  part  that  formed  the  pod  of  the  bean  with 

its  contained  seeds.      The  corn  grain  is  a  fruit  and  not  a  seed. 

Structure  of  a  Grain  of  Corn.  —  Examina- 
tion of  a  well-soaked  grain  of  corn  discloses 

a  difference  in  the  two  flat  sides  of  the  grain. 

A  light-colored  area  found  on   one    surface 

marks  the  position  of  the  embryo;  the  rest 

of  the  grain  contains  the  food  supply.     The 

scar  marking  the  former  attachment  of  the 

silk  is  found  near  the  outer  edge  of  the  grain. 
A  grain  cut  lengthwise  perpendicular  to 

the  flat  side  and  then  dipped  in  weak  iodine 

shows  two  distinct  parts,  an  area  containing 

considerable  starch,  the  endosperm,  and  the 

embryo  or  young  plant.     Careful  inspection 

shows  the  hypocotyl  and  plumule  (the  latter 

pointing  toward  the  free  end  of  the  grain) 

and  a  part  surrounding  them,  the  single  coty- 
ledon (see  Figure).      Here  again  we  have  an 

example  of  a  fitting  for  future  needs,  for  in 

this  fruit  the  one  seed  has  at  hand  all  the 
food  material  necessary  for 
rapid  growth,  although  the 
food  is  here  outside  the  em- 
bryo. 

Endosperm  the  Food  Sup- 
ply of  Corn.  —  We  do  not  find 

that  the  one  cotyledon  of  the    Longitudinal   section   of 

A  grain  of  corn,  ^^^^        j^^  serves  the   Same     yo^°«  ^^^  of  ^o'""  •  ^' 

cut    Icncrt'liwisc  * 

c,    cotyledon!  purpose  to  the  young  plant 

E,  endosperm;    aS  did  the  twO  COtylcdouS  of 

p  ^^^e°*^^'  ^^^  ^^^^'  Although  we  find 
a  little  starch  in  the  corn 
cotyledon,  still  it  is  evident  from  our  tests  that  the  endosperm  is 
the  chief  source  of  food  supply.  The  study  of  a  thin  section  of 
the  corn  grain  under  the  compound  microscope  shows  us  that  the 
starch  grains  in  the  outer  part  of  the  endosperm  are  large  and 
regular  in  size.     Those  near  the  edge  of  the  cotyledon  are  much 


the  fruits ;  S,  the  stig- 
mas ;  SH,  sheathlike 
leaves ;  ST,  the  flower 
stalk  or  peduncle. 
(After  Sargent.) 


70 


SEEDS  AND  SEEDLINGS 


smaller  and  quite  irregular,  having  large  holes  in  them.  We  know 
that  the  germinating  grain  has  a  much  sweeter  taste  than  that 
which  is  not  growing.  This  is  noticed  in  sprouting  barley  or 
malt.  We  shall  later  find  that,  in  order  to  make  use  of  starchy- 
food,  a  plant  or  animal  must  in  some  manner  change  it  over  to 
sugar.  This  change  is  necessary,  because  starch  cannot  be  ab- 
sorbed by  the  young  plant,  while  sugar  can  be  thus  taken  in. 


'"■'^,fKi"J'''t  '"*^*''^^"%s--  It ''    ' ''■' 

/ 

m 

%  :■ 

p   ,  ,^M-r.^ 

\  i\ 

MBl^ll 

».V 

\'ly< 

A  cornfield,  showing   staminate  and   pistillate   flowers,    the  latter  having  become 

grains  of  corn. 

A  Test  for  Grape  Sugar.  —  Place  in  a  test  tube  the  substance  to 
be  tested  and  heat  it  in  a  little  water  so  as  to  dissolve  the  sugar. 
Add  to  the  fluid  twice  its  bulk  of  Fehhng's  solution,^  which  has  been 

1  To  make  Fehling's  solution  (so-called  after  its  discoverer),  add  to  35  grams  of 
copper  sulphate  (blue  vitriol)  500  c.c.  of  water.  Put  aside  until  it  is  completely- 
dissolved.     Call  this  solution  No.  1. 

To  160  grams  of  caustic  soda  and  173  grams  of  Rochelle  salt  add  500  c.c.  of 
water.     Call  this  solution  No.  2. 

For  use  mix  equal  parts  of  solution  1  and  2. 

The  following  formula  is  also  convenient :  — 
I.    Copper  sulphate :   9  grams  in  250  c.c.  water. 
II.    Sodium  hydroxide :    30  grams  in  250  c.c.  water. 

Ill,    Rochelle  salt :    43  grams  in  250  c.c.  water. 

For  use  add  to  equal  parts  I,  II,  and  III,  two  parts  of  water. 


SEEDS  AND  SEEDLINGS  71 

previously  prepared.  Heat  the  mixture,  which  should  now  have 
a  blue  color,  in  the  test  tube.  If  grape  sugar  is  present  in  consid- 
erable quantity,  the  contents  of  the  tube  will  turn  first  a  greenish, 
then  yellow,  and  finally  a  brick-red  color.  Smaller  amounts  ^vill 
show  less  decided  red.  No  other  substance  than  sugar  will  give 
this  reaction.  If  Benedict's  test^  is  used,  a  colored  precipitate 
will  appear  in  the  test  tube  after  boiling. 

Starch  changed  to  Grape  Sugar  in  the  Corn.  —  That  starch  is 
being  changed  to  grape  sugar  in  the  germinating  corn  grain  can 
easily  be  shown  if  we  cut  lengthwise  through  the  embryos  of  half 
a  dozen  grains  of  corn  that  have  just  begun  to  germinate,  place 
them  in  a  test  tube  with  some  Fehling's  solution,  and  heat  almost 
to  the  boiling  point.  They  will  be  found  to  give  a  reaction  show- 
ing the  presence  of  sugar  along  the  edge  of  the  cotyledon  and 
between  it  and  the  endosperm. 

Digestion.  —  This  change  of  starch  to  grape  sugar  in  the  corn 
is  a  process  of  digestion.     If  you  chew  a  bit  of  unsweetened  cracker 

*  Benedict's  Test  for  Grape  Sugar 

This  test,  known  from  its  author  as  "Benedict's  test,"  will  be  found  described 
in  the  1909  edition  of  Hawk's  Biochemical  Chemistry.  In  the  latter  it  is  the  one 
labeled  "Second  Solution." 

preparation 

Copper  sulphate 17.3  grama 

Sodium  citrate 173.    grams 

Sodium  carbonate  (anhydrous)     .         .         .     100.    grams 
Make  up  to  1  liter  with  distilled  water 

With  the  aid  of  heat  dissolve  the  sodium  citrate  and  carbonate  in  about  600  c.o. 
of  water.  Pour  through  folded  filter  paper  into  a  glass  graduate  and  make  up  to 
850  c.c.  with  distilled  water. 

Dissolve  the  copper  sulphate  in  about  100  c.c.  of  water  and  make  up  to  150  c.c. 
with  distilled  water. 

Pour  the  carbonate-citrate  solution  into  a  large  beaker  or  casserole  and  add 
the  copper  sulphate  solution  slowly  with  constant  stirring. 

The  mixed  solution  is  ready  for  use  and  does  not  deteriorate  on  standing. 

For  use  add  to  5  c.c.  of  the  solution  in  a  test  tube  8  drops  (more  does  not  disturb 
the  experiment,  but  8  drops  is  suflBcient  for  a  good  result)  of  the  solution  under 
examination.  Boil  for  one  or  two  minutes  and  let  cool.  If  grape  sugar  be  present, 
the  entire  body  of  the  liquid  will  be  filled  with  a  precipitate  which  may  be  red, 
yellow,  or  green  in  color,  depending  upon  the  amount  of  sugar  present.  Eight 
drops  of  1  per  cent  dextrose  will  yield  precipitates  of  large  amounts. 

The  positive  reaction  is  the  precipitate,  not  the  color.  On  this  account  the  test 
may  be  applied  as  well  in  artificial  light  as  in  daylight. 


72 


SEEDS  AND  SEEDLINGS 


in  the  mouth  for  a  Httle  time,  it  will  begin  to  taste  sweet,  and  if  the 
chewed  cracker,  which  we  know  contains  starch,  is  tested  with 
Fehling's  solution,  some  of  the  starch  will  be  found  to  have  changed 
to  grape  sugar.  Here  again  a  process  of  digestion  has  taken 
place.  In  both  the  corn  and  in  the  mouth,  the  change  is  brought 
about  by  the  action  of  peculiar  substances  known  as  digestive 
ferments,  or  enzymes,  and  the  result  is  that  substances  which 
before  digestion  would  not  dissolve  in  water  now  will  dissolve. 

The  Action  of  Diastase  on  Starch.  —  The  enzyme  found  in  the 
cotyledon  of  the  com,  which  changes  starch  to  grape  sugar, 
is  called  diastase.  It  may  be  separated  from  the  cotyledon  and 
used  in  the  form  of  a  powder. 

To  a  little  starch  in  half  a  cup  of  water  we  add  a  very  httle  (1 
gram)  of  diastase  and  put  the  vessel  containing  the  mixture  in  a 
warm  place,  where  the  temperature  will  remain  nearly  constant  at 
about  98°  Fahrenheit.     On  testing  part  of  the  contents  at  the  end 

of  half  an  hour,  and  the 
remainder  the  next  morn- 
ing, for  starch  and  for 
grape  sugar,  we  find  from 
the  latter  test  that  the 
starch  has  been  almost 
completely  changed  to 
grape  sugar.  Starch  and 
warm  water  under  similar 
conditions  will  not  react 
to  the  test  for  grape  sugar. 


Germinating  corn  grains, 
if  deprived  of  their  endos- 
perm, soon  die.  But  if  the 
endosperm  is  removed  and  a 
little  com  starch  paste  be 
stuck  to  the  little  plant  in 
place  of  the  endosperm,  the 

development  of  the  embryo  will   be   but   little   affected  (see  Figure). 

Evidently  the  enzyme  formed  in  the  cotyledon  has  the  power  to  digest 

the  starch  paste,  and  the  cotyledon  transfers  the  digested  food  to  the 

growing  parts  of  the  embryo. 


The  use  of  the  endosperm  to  the  corn  :  A ,  seed- 
lings without  endosperm ;  B,  seedlings  with 
starch  in  place  of  endosperm;  normal  seed- 
lings at  the  center. 


SEEDS  AND  SEEDLINGS 


78 


Other  Foods  in  Corn  Grain.  —  Other  foods  besides  starch  and 
sugar  are  present  in  the  corn  grain.  A  test  for  proteid  shows  that 
a  considerable  amount  of  this  food  is  present.  Oil  also  is  found. 
In  the  sweet  corn  that  we  eat  water  forms  a  very  large  percentage 
of  its  composition  by  weight. 

Monocotyledons,  Dicotyledons,  and  Polycotyledons.  —  Plants 
that  boar  seeds  having;  but  a  single  cotyledon  are  called  monocoty- 


A  hardwood  forest  showing  representative  di- 
cotyledonous trees. 


A  pine  seedling. 
Note  the  number 
of  cotyledons. 


ledons.  (What  are  some  other  characteristics  ?)  Although  we  find 
a  good  many  monocotyledonous  plants  in  this  part  of  the  world,  this 
group  is  characteristic  of  the  tropics,  just  as  the  dicotyledons  are 
the  type  for  the  temperate  climate.  Sugar  cane  and  many  of  the 
large  trees,  such  as  the  date  palm,  pahnetto,  and  banana,  are  ex- 
amples. Among  the  common  monocotyledons  of  the  north  tem- 
perate zone  are  corn,  hly,  hothouse  smilax,  and  asparagus.  Dicot- 
yledons or  plants  having  two  cotyledons  in  the  seed  are  those  with 


74 


SEEDS  AND  SEEDLINGS 


A  spruce  cone  ;  the  seeds  are  held  under  the 
scales  of  the  cone,  one  of  which  is  shown 
removed. 


which  we  come  most  in  contact  in  daily  life.  Many  of  om*  garden 
vegetables,  peas,  beans,  squash,  melons,  etc.,  all  of  our  great  hard- 
wood forest  trees,  beech,  oak, 
birch,  chestnut  and  hickory, 
used  for  the  '  trim '  of  houses, 
all  of  our  fruit  trees,  pears, 
apples,  peaches,  and  plums, 
and,  in  fact,  a  very  large 
proportion  of  all  plants  living 
in  the  north  temperate  zone 
are  dicotyledons. 

A  third  type  of  plant, 
grouped  according  to  the 
number  of  cotyledons,  is  the 
group  called  the  polycoty- 
ledons,  represented  by  the 
pines  dnd  their  kin.  Such 
plants  furnish  most  of  the  lumber  and  shingles  used  in  the  con- 
struction of  frame  houses.  The  soft  woods  (as  the  pines,  hemlocks, 
spruces,  and  other  "  evergreens  ")  are  also  of  much  value  in  the 
manufacture  of  paper.  The  wood-pulp  industry  has  grown  to 
such  proportions  as  to  be  a  menace  to  our  softwood  forests. 

Problem  XI.  A  study  of  the  factors  necessary  for  awaheniivg 
{germinating)  the  embryo  within  the  seed.  {Laboratory  Man- 
ZLoZ,  Prob.  XL) 

(a)    Moisbwre, 

Qi)    Temperature. 

(c)    Oxygen. 

(S>    Food. 

External  Factors  which  determine  the  Growth  of  Seeds.^  —  We 
know  that  a  dry  seed,  after  lying  dormant  and  apparently  dead 
for  months  and  sometimes  for  years,  will,  when  the  proper  stimuli 
are  appUed  to  it,  start  in  its  growth  into  a  new  plant.  Something 
from  outside  the  seed  must  evidently  start  the  growth  of  the  little 
embryo  within  the  seed  coats.     There  are  several  factors  which 

1  In  making  a  series  of  experiments  it  is  important  to  keep  the  conditions  uni- 
fonn,  varying  only  the  one  we  are  testing. 


SEEDS  AND   SEEDLINGS 


75 


are  absolutely  necessary  for  germination.     One  of  these  factors 
is  the  presence  of  a  certain  amount  of  moisture. 

Water  a  Factor.  —  We  can 
prove  that  the  bean  seed  will 
take  up  a  considerable 
amount  of  water  and  that 
it  swells  during  the  process. 
Fill  a  flowerpot  or  a  thin 
glass  bottle  almost  to  the 
top  with  dry  beans,  cover 
securely  as  shown  in  the 
illustration,  and  place  in 
water  overnight.  The  force 
exerted  by  the  swelling  seeds 
is  sufficient  to  break  the 
flowerpot  or  bottle.  It  is 
easy  to  prove  that  a  dry  seed  wiU  not  germinate.  The  exact 
amount  of  water  which  is  most  favorable  for  the  germination  of 
a  seed  can  bo  clctorniinod  only  by  careful  experiment.     In  a  very 


The  expansive  force  of  germinating  seeds. 
The  flowerpot  to  the  left  was  filled  with 
dry  beans,  a  block  of  wood  wired  on,  and 
the  whole  apparatus  placed  in  a  pail  of 
water  overnight.  The  result  is  shown  at 
the  right. 


Effect  of  water  upon  the  growth  of  trees. 
The  trees  were  all  planted  at  the  same  time  in  soil  that  is  sandy  and  uniform.    They 
are  irrigated  by  a  small  stream  running  from  left  to  right.    Most  of  the  water 
soaks  in  before  reaching  the  last  trees. 


76 


SEEDS  AND  SEEDLINGS 


general  way  it  may  be  said  that  an  oversupply  of  water  will  pre- 
vent growth  of  seeds  almost  as  effectually  as  no  water  at  all.  In  gen- 
eral the  amount  most  favorable  for  germination  is  a  moderate  supply. 
We  shall  find  that  although  plants  may  live  for  a  consider- 
able time  in  water  or  in  sawdust  or  other  materials  well  moistened 
in  water,  yet  soil  is  an  essential  to  the  growth  of  most  seed  plants. 
Some  plants,  as  some  orchids  and  "  Spanish  moss  "  (a  true  seed 
plant),  may  exist  without  any  connection  with  soil.  Yet  most 
plants  need  soil  water  and  take  from  the  soil  materials  needed  to 
make  up  their  living  matter. 

Moderate  Temperature  Best.  —  Another  factor  influencing  the 
germination  of  seeds  is  that  of  temperature.  The  temperature  at 
which  different  seeds  germinate  varies  greatly.  Those  of  you 
who  have  a  garden  at  home  know  that  even  some  varieties  of  seeds 
germinate  at  lower  temperatures  than  others  of  the  same  species ; 
for  example,  early  peas,  lettuce,  or  radish  seed.  As  a  general  rule, 
increase  in  temperature  is  favorable  up  to  a  certain  point,  beyond 
which  it  is  injurious  to  the  young  plant,  and  seeds  exposed  to  a  mod- 
erate temperature  do  better  in  the  long  run  than  those  in  the  heat. 
Light  has  a  certain  marked  effect  on  young  seedlings,  which 

will  be  considered  when  we  take  up 
the  growth  of  the  stem  in  more 
detail. 

Some  Part  of  the  Air  a  Factor.  — 
We  have  already  considered  the 
chemical  composition  of  the  air  in 
its  place  as  part  of  the  environment 
of  plants  and  animals.  But  few  of 
us  reason  out  why  air  is  a  necessary 
factor  in  the  growth  of  plants  and 
animals. 

It  is  an  easy  matter  to  prove  that 
peas  or  beans  will  not  germinate 
without  a  supply  of  air.  Equal 
numbers  of  soaked  peas,  placed  in 
two  bottles,  one  tightly  stoppered,  the  other  having  no  stopper, 
both  bottles  being  exposed  to  identical  conditions  of  light,  tem- 
perature, and  moisture,  show  that  the  seeds  in  both  bottles  start 


Experiment  to  show  the  effect  of  lack 
of  air  on  germination. 


SEEDS  AND  SEEDLINGS 


77 


to  germinate,  but  that  those  in  the  closed  bottle  soon  stop  while 
those  in  the  open  jar  continue  to  grow  almost  as  well  as  similar 
seeds  placed  in  an  open  dish  would  do. 

Why  did  not  the  seeds  in  the  covered  jar  germinate?  We  have 
seen  that  to  release  the  energy  contained  in  a  piece  of  coal  we 
must  burn  or  oxidize  it.  To  do  this  we  must  have  a  constant 
supply  of  fresh  air  containing  oxygen.  The  seed,  in  order  to  re- 
lease the  energy  locked  up  in  its  food  supply,  must  have  oxygen, 
so  that  the  oxidation  of  the  food  may  take  place.  Hence  a  con- 
stant supply  of  fresh  air  is  an  important  factor  in  gennination.  It 
is  important  that  air  should  penetrate  between  the  grains  of  soil 
around  a  seed.  The  frequent  stirring  of  the  soil  enables  the  air 
to  reach  the  seed.  Air  helps  break  down  (oxidizes)  some  materials 
in  the  soil  and  puts  them  in  a  form  that  the  germinating  seed  can 
use.  This  necessity  for  oxygen  shows  us  at 
least  one  reason  why  the  farmer  plows  and 
harrows  a  field  and  one  important  use  of  the 
earthworm. 

Food  oxidized  in  the  Germinating  Seed.  — 
But  can  it  be  proved  that  food  substances  are 
burned  up  during  the  germination  of  the  seeds  ? 
To  answer  this  question  let  us  carefull}^  re- 
move the  stopper  from  the  stoppered  jar  and 
insert  a  Hghted  candle.  The  candle  goes  out 
at  once.  The  surer  test  of  limewater  shows  the 
presence  of  carbon  dioxide  in  the  jar.  The 
carbon  of  the  foodstuffs  of  the  pea  united  with 
the  oxygen  of  the  air,  forming  carbon  dioxide. 
Growth  stopped  as  soon  as  the  oxygen  was  ex- 
hausted. The  presence  of  carbon  dioxide  in 
the  jar  is  an  indication  that  a  very  important 
process  which  we  associate  with  animals  rather  than  plants,  that 
of  respiration,  is  taking  place. 

I^roblem  XTI.    A  study  of  yoitng  plants  until  they  are  inde- 
pendent (^seedlings).    {Laboratory  Manual,  Proh.  XII,) 

Gennination.  —  If  you  plant  a  nimiber  of  soaked  kidney  beans 
in  damp  soil  or  sawdust  and  at  the  end  of  each  day  remove  a  single 


t 


The  lim  ewater  test ;  the 
tube  at  the  right 
shows  the  effect  of 
carbon  dioxide. 


78 


SEEDS  AND   SEEDLINGS 


seedling,  you  will  be  able  to  obtain  a  complete  record  of  the  growth 
of  the  kidney  bean.     The  first  signs  of  germination  are  the  break- 


A  series  of  early  stages  in  the  germination  of  a  kidney  bean. 

ing  of  the  testa  and  the  pushing  outward  of  the  hypocotyl  to  form 
the  first  root.  A  little  later  the  hypocotyl  begins  to  curve  down- 
ward. A  later  stage  shows  the  hypocotyl  lifting  the  cotyledon 
upward.     In  consequence  the  hypocotyl  forms  an  arch,  dragging 

after  it  the  bulky  cotyledons. 
The  stem,  as  soon  as  it  is 
released  from  the  ground, 
straightens  out.  From  be- 
tween the  cotyledons  the  bud- 
like plumule  or  epicotyl  grows 
upward,  forming  the  first  true 
leaves  and  all  of  the  stem 
above  the  cotyledons.  As 
growth  continues,  we  notice 
that  the  cotyledons  become 
smaller  and  smaller,  until 
eventually  their  food  contents 
having  been  absorbed  into  the 
young  plant,  they  dry  up  and 
may  fall  off.  The  young 
plant  is  now  able  to  care  for 

Bean  seedlings      Note  that  in   the   older      j^^^j^  ^^^  ^^  ^^-^  ^^  ^^^^ 

seedlings  at  the  left  the  cotyledons  have  *^ 

been  alnjost  entirely  used  up.  passed   through   the   stages   of 


SEEDS   AND   SEEDLINGS 


79 


germination.  All  the  stages 
passed  through  by  the  young 
plant,  from  the  time  the  seed  be- 
gins to  sprout  until  it  cari  take 
care  of  itself  by  means  of  its 
roots  and  leaves,  are  known  as 
the  stages  of  germination. 

In  the  pea,  growth  is  like- 
wise at  first  made  largely  at 
the  expense  of  the  cotyledons, 
which  never  rise  alxjve  ground. 
Removal  of  the  cotyledons  from 
half  the  number  of  one  lot  of 
germinating  peas,  and  exposure 
to  the  same  conditions  as  the 
other  half  of  the  same  lot,  shows 
that  the  loss  of  the  cotyledons 
retards  growth  and  may  result 
in  the  death  of  the  seedlings.^ 


Experinu'nt  to  show  the  function  of  the 
cotyledons  of  the  pea,  photographed  at 
the  end  of  two  weeks.  Note  the  size  of 
the  plants  at  the  left,  without  cotyle- 
dons. 


Cotyledons  as  Foliage  Leaves.  —  In  the  young  plants  which  we  have 
just  been  studying,  the  cotyledons  hold  a  reserve  food  supply,  but 
do  not  serve  at  any  time  as  true  leaves  for  the  plant.  In  many  dicoty- 
ledons, however,  the  seed 


leaves  do  act  as  true 
leaves.  This  may  well  be 
seen  in  the  squash  seed- 
ling. Here  the  young 
plant  has  little  or  no  Jood 
stored  in  the  cotyledons; 
it  must  be  prepared  to 
take  care  of  itself  quickly. 
It  does  this  by  means  of 
the  rapidly  growing  coty- 
ledons, which  soon  unfold  as  true  leaves  to  the  sun. 

In  the  seeds  of  the  pea  and  bean  we  have  found  that  the  embryo  takes 
up  all  the  space  within  the  seed  coats.  There  are  some  dicotyledonous 
plants  that  have  food  stored  outside  of  the  embryo.  Such  a  plant  is  the 
castor  bean.     A  section  cut  vertically  through  the  castor  bean  discloses 


Arrangement  of  embryo  in  endosperm  (Gray)  : 
a,  morning-glory ;  6,  barberry ;  c,  potato ;  d,  four- 
o'clock. 


*  It  must  be  remembered  that  this  is  not  quite  a  fair  test  to  the  pea,  because  we 
take  away  from  the  young  plant  part  of  its  own  body. 


80 


SEEDS  AND  SEEDLINGS 


a  white  oily  mass  directly  under  the  seed  coats.  This  mass  is  called  the 
endosperm.  If  it  is  tested  with  iodine,  it  will  be  found  to  contain  starch ; 
oil  is  also  present  in  considerable  quantity.  Within  the  endosperm  Ues 
the  embryo,  a  thin,  whitish  structure. 

The  Uses  of  Seeds.  —  Not  only  does  a  seed  serve  to  continue 
a  species  of  plant  in  a  certain  locality,  but  it  serves  to  give  the  plant 
a  foothold  in  new  places.  This  can  be  done,  as  we  shall  see  later, 
to  a  limited  degree  by  cuttings,  grafting,  and  in  other  ways,  but  the 
usual  way  is  by  the  production  and  planting  of  seeds.  Seeds  may 
be  blown  by  the  wind  or  carried  by  animals,  or  by  a  hundred  de- 
vices work  their  way  to  pastures  new,  there  to  establish  outposts 
of  their  kind. 

Immense  numbers  of  seeds  may  be  produced  by  a  single  plant. 
This  may  be  of  great  economic  importance.  A  single  pea  plant 
may  produce  twenty  pods,  each  containing  from  six  to  eight  seeds. 
This  would  mean  the  possibility  of  nearly  twenty-five  thousand 

plants  produced  from  the 
original  parent  by  the  end 
of  the  second  season  and 
the  rapid  production  of  a 
source  of  food  for  man- 
kind. A  plant  of  Indian 
corn  may  produce  over 
fifteen  hundred  grains  of 
corn.  On  the  other  hand, 
many  weeds  produce  seed 
in  still  greater  numbers. 
A  single  capsule  of  Jimson 
weed  has  been  found  to 
hold  over  six  hundred 
seeds.  A  single  milkweed 
The  thistle  is  even  more 


Milkweed  fruit,  showing  method  of  seed  dispersal. 


may  set  free  over  two  thousand  seeds, 
prolific. 

Some  seeds,  especially  those  of  weeds,  are  able  to  withstand 
great  extremes  of  heat  and  cold  and  still  to  retain  their  ability  to 
germinate.  Some  have  been  known  to  retain  their  vitality  for 
over  fifty  years.  In  plants,  the  seeds  of  which  show  unusual 
hardiness,  it  is  foimd  that  the  food  supply  is  often  so  placed  as 


SEEDS  AND  SEEDLINGS  81 

to  protect  the  delicate  parts  of  the  embryo  from  injury.  The  food 
is  in  a  form  not  easily  dissolved  by  water  or  broken  up  by  the 
action  of  frost,  so  that  it  is  kept  in  a  hard  state  until  such  a  time 
as  it  can  be  softened  by  the  process  of  digestion  during  the  growth 
of  the  plant.  It  can  be  seen  that  plants  bearing  seeds  having 
some  of  the  above  characters  have  a  great  advantage  over  plants 
bearing  seeds  that  are  poorly  protected. 

Prohle^n  XIII,  A  study  of  some  methods  of  plant  breeding. 
{.Laboratory  Manual,  Proh,  XIII.) 

Plant  Breeding :  Variation  of  Plants.  —  Examination  of  a  row 
of  plants  in  a  garden,  of  a  hundred  dandelion  plants,  or  careful 
measurements  made  on  the  pupils  in  a  classroom,  would  show  us 
that  no  two  plants  and  no  two  boys  or  girls  have  exactly  the  same 
measurements  or  characters.  Each  plant  or  animal  in  a  state  of 
nature  tends  to  vary  somewhat  from  its  parent.  This  is  a  law 
among  plants  and  animals. 

But  a  second  law  exists  which  we  also  know  something  about. 
A  plant  or  animal  hands  down  to  its  offspring  some  of  the  charac- 
teristics which  it  possesses.  Each  one  of  us  in  some  way  resembles 
our  parents  or,  it  may  be,  our  grandparents.  Each  plant  produced 
from  seed  will  be  in  some  respects  like  the  plant  which  produced 
the  seed. 

These  two  laws,  of  variation  and  of  heredity,  the  bases  on  which 
Charles  Darwin  explained  his  theory  of  evolution,  are  made  use 
of  by  plant  and  animal  breeders.  Since  plants  tend  to  vary  and 
since  such  variations  may  be  continued  in  their  offspring,  plant 
breeders  have  helped  nature  by  artificially  selecting  and  propa- 
gating the  plants  showing  the  characters  wanted. 

Selective  Planting.  —  By  selective  planting  we  mean  choosing 
the  best  plants  and  planting  the  seed  from  these  plants  with  a  view  of 
improving  the  yield.  In  doing  this  we  must  not  necessarily  select 
the  most  perfect  fruits  or  grains,  but  must  select  seeds  from  the 
best  plants.  A  wheat  plant  should  be  selected  not  from  its  yield 
alone,  but  from  its  ability  to  stand  disease  and  unfavorable  con- 
ditions. In  1862  a  Mr.  Fultz,  of  Pennsylvania,  found  three  heads 
of  beardless  or  bald  wheat  while  passing  through  a  large  field  of 
bearded  wheat.     He  picked  them  out,  sowed  them  by  themselves, 

HUNT.  ES.  BIO.  —  6 


82 


SEEDS  AND  SEEDLINGS 


Improvement  of  corn  by  selection  :  a,  improved  type  ; 
b,  original  type  from  which  it  was  developed. 


and  produced  a  quantity  of  wheat  now  known  favorably  all  over 
the  world  as  the  Fultz  wheat.      By  careful  seed  selection,  some 

Western  farmers  have 
increased  their  wheat 
production  by  25  per 
cent.  This,  if  kept  up 
all  over  the  United 
States,  would  mean 
over  $100,000,000  a 
year  in  the  pockets  of 
the  farmers. 

Boys  and  girls  who 
have  gardens  of  their 
own  can  easily  try 
experiments  in  selec- 
tion with  almost  any 
garden  vegetable.  Corn  is  one  of  the  best  plants  to  experiment 
with.  Gather  for  planting  only  the  fullest  ears  and  those  with  the 
largest  kernels.  You  must  also  select  from  the  plants  those  that 
produce  the  most  ears.  Plant  such  corn  grains,  carefully  selected, 
in  a  plot  by  themselves  in  the  garden,  and  compare  their  yield 
with  that  of  the  nonselected  corn.  The  accompanying  picture 
shows  what  can  be  done  by  selection.  Plants  thus  produced 
may  become  in  time  varieties  of  the  original  species  from  which 
they  came. 

Hybridizing.  —  We  have  already  seen  that  pollen  from  one  flower 
may  be  carried  to  another  of  the  same  species,  thus  producing  seeds. 
If  pollen  from  one  plant  be  placed  on  the  pistil  of  another  of  an 
allied  species  or  variety,  fertilization  may  take  place  and  new 
plants  be  eventually  produced  from  the  seeds.  Such  plants  are 
called  hybrids. 

Hybrids  are  extremely  variable  and  often  are  apparently  quite 
unlike  either  parent  plant.  Such  are  some  of  the  results  of  Luther 
Burbank's  work  with  the  hybrid  plums,  the  Department  of  Agri- 
culture experiments  in  the  crossing  of  oranges  and  lemons  and  the 
formation  of  thousands  of  new  varieties  of  garden  plants  of  various 
kinds  —  beans,  peas,  tomatoes,  and  the  like. 

By  far  the  greatest  possibilities  to  the  farmer  or  fruit  grower 


SEEDS  AND  SEEDLINGS  83 

seem  to  come  from  hybridizing.  Of  recent  years  new  theories  have 
been  advanced  accounting  for  the  variation  and  heredity  of  plants 
and  animals.  One,  by  a  Dutchman  named  Hugo  de  Vries,  is 
that  new  species  of  plants  and  animals  arise  suddenly  by  "  muta- 
tions "  or  steps.  This  means  that  new  species  instead  of  arising 
from  very  slight  variations,  continuing  during  long  periods  of  years 
(as  Darwin  beheved),  might  arise  very  suddenly  as  a  very  great 
variation  which  would  at  once  breed  true.  It  is  easily  seen  that 
such  a  condition  would  be  of  immense  value  to  breeders,  as  new 
plants  or  animals  quite  unlike  their  parents  might  thus  be  formed 
and  perpetuated.  It  will  be  the  future  problem  of  plant  breeders 
to  isolate  and  breed  "  mutants,"  as  such  plants  are  called.^ 

RSFEBENCB  BoOKS 
ELEMENTARY 

Sharpe,  A  Laboratory  Manual  for  the  Solution  of  Problems  in  Biology.     American 

Book  Company. 
Andrews,  Botany  all  the  Year  Round,  pages  103-119.     American   Book   Company. 
Atkinson,  First  Studies  of  Plant  Life,  Chaps.  I,  II,  III,  XXV.     Ginn  and  Company. 
ComeU    Nature    Study   Leaflets,   XXVIII,    XLII,  XLIV.      N.Y.    Department  of 

Agriculture. 
Dana,  Plants  and  their  Children,  pages  50-98.     American  Book  Company. 
Harwood,  New  Creations  in  Plant  Life.     The  Macmillan  Company. 

ADVANCED 

Coulter,  Barnes,  and  Cowles,  A  Textbook  of  Botany,  Part  II.  American  Book  Com- 
pany. 

De  Candolle,  Origin  of  Cultivated  Plants.    D.  Appleton  and  Company. 

De  Vries,  Species  and  Varieties,  edited  by  D.  T.  MacDougal.  Open  Court  Pub- 
lishing Company. 

Farmers'  Bulletin,  229. 

Goodale,  Physiological  Botany.     American  Book  Company. 

MacDougal,  Plant  Physiology.     Longmans,  Green,  and  Company. 

Punnett,  R.  C,  Mendelism.     Cambridge,  England. 

Thompson,  Heredity.     John  Murray,  London. 

University  of  Illinois  Agricultural  Station,  Bulletin  87. 

University  of  Minnesota  Agricultural  Station,  Bulletin  165. 

Wallace,  Darwinism.     The  Macmillan  Company. 

Yearbook,  U.S.  Department  of  Agriculture. 

^  The  part  played  by  Mendel's  law  is  too  difficult  to  explain  to  high-school  pupils. 
For  a  well-organized  statement  of  recent  work,  see  Bailey's  P^nt  Breeding  or 
"The  Relation  of  Certain  Biological  Principles  to  Plant  Breeding  "  E.  M.  East, 
Bulletin  158,  Conn.  Agri.  Exp.  Station,  New  Haven,  Conn. 


VII.   ROOTS  AND  THEIR  WORK 


JProhlem  XIV.    A  study  of  roots.    {Laboratory  Manual,  Prob. 

xir.) 

(a)    Factors  influencing  direction  of  growth. 

(&)    Structure. 

(c)    How  they  absorb  soil  water. 

The  development  of  a  bean  seedling  has  shown  us  that  the  root 
invariably  grows  first.  One  of  the  most  important  functions  of  the 
root  to  a  young  seed  plant  is  that  of  a  holdfast,  an  anchor  to  fasten  it  in 

the  place  where  it  is  to  develop.  In 
this  chapter  we  shall  find  many 
other  uses  of  the  root  to  the  plant, 
the  taking  in  of  water  and  the 
mineral  and  organic  matter  dis- 
solved therein,  the  storage  of  food, 
chmbing,  etc.  All  other  functions 
than  the  first  one  stated  arise  after 
the  young  plant  has  begun  to 
develop. 

Root  System.  —  If  you  dig  up  a 
young  bean  seedling  and  carefully 
wash  off  the  roots,  you  will  see  that 
a  long  root  is  developed  as  a  con- 
tinuation of  the  hypocotyl.  This 
root  is  called  the  primary  root. 
Other  smaller  roots  which  grow 
from  the  primary  root  are  called  secondary,  or  tertiary,  depending 
on  their  relation  to  the  first  root  developed. 

Downward  Growth  of  Root.  Influence  of  Gravity.  — Most  of  the 
roots  examined  take  a  more  or  less  downward  direction.  We  are 
all  familiar  with  the  fact  that  the  force  we  call  gravity  influences  life 
upon  this  earth  to  a  great  degree.  Does  gravity  act  on  the  grow- 
ing root  ?    This  question  may  be  answered  by  a  simple  experiment. 

84 


i' 

M 

^ 

m 

^. 

.-^ 

1   y/ ;     / 

i       \ 

V 

A  root  system,  showing  primary  and 
second  roots. 


ROOTS  AND   THEIR   WORK 


85 


Plant  mustard  or  radish  seeds  in  a  pocket  garden,  place  it  on 
one  edge  and  allow  the  seeds  to  germinate  until  the  root  has  grown 
to  a  length  of  about  half  an  inch.  Then  turn  it  at  right  angles 
to  the  first  position  and  allow  it  to 
remain  for  one  day  undisturbed.  The 
roots  now  will  be  found  to  have  turned 
in  response  to  the  change  in  posi- 
tion, that  part  of  the  root  near  the 
growing  point  being  the  most  sensitive 
to  the  change.  This  experiment  seems 
to  indicate  that  the  roots  are  influenced 
to  grow  downward  by  the  force  we 
call  gravity.^ 

The  reaction  of  the  plant  {or  any  living 
thing)  to  this  force  is  called  geotropisni. 
Roots  are  stimulated  by  gravity  to  grow 
downward;  hence  they  are  said  to  he 
positively  geotropic. 

Experiments  to  determine  Influence 
of  Moisture  on  a  Growing  Root. — The 
objection  might  well  be  interposed  that 
possibly  the  roots  in  the  pocket  garden  grew  downward  after 
water.  That  moisture  has  an  influence  on  the  growing  root  is 
easily  proved. 

Plant  bird  seed  and  the  seed  of  mustard  or  radish  in  the  under- 
side of  a  sponge,  which  should  be  kept  wet,  and  may  be  sus- 
pended by  a  string  under  a  bell  jar  in  the  schoolroom  window. 
Note  whether  the  roots  leave  the  sponge  to  grow  downward,  or 
if  the  moisture  in  the  sponge  is  sufficient  to  counterbalance  the 
force  of  gravity. 


Revolve  this  Figure  in  the  direc- 
tion of  the  arrows  to  see  if 
the  roots  of  the  radish  respond 
to  gravity. 


*  The  Pocket  Garden.  —  A  very  convenient  form  of  pocket  germinator  may  be 
made  in  a  few  minutes  in  the  following  manner :  Obtain  two  cleaned  four  by  five 
negatives  (window  glass  will  do) ;  place  one  flat  on  the  table  and  place  on  the  glass 
half  a  dozen  pieces  of  colored  blotting  paper  cut  to  a  size  a  little  less  than  the  glass. 
Now  cut  four  thin  stiips  of  wood  so  as  to  fit  on  the  glass  just  outside  of  the  paper. 
Next  moisten  the  blotter,  place  on  it  some  well-soaked  radish  or  mustard  seeds  or 
grains  of  barley,  and  cover  it  with  the  other  glass.  The  whole  box  thus  made  should 
be  bound  together  with  bicycle  tape.  Seeds  will  germinate  in  this  box,  and  with 
care  may  live  for  two  weeks  or  more. 


86 


ROOTS  AND   THEIR  WORK 


Another  experiment  is  the  following :  Divide  the  interior  of  a  shallow 
wooden  box  into  two  parts  by  an  incomplete  partition.  Partly  fill  the  box 
with  sawdust  and  place  the  opening  in  the  partition  so  that  it  is  below  the 
surface  of  the  sawdust.  Plant  peas  and  beans  in  the  sawdust  on  one  side 
of  the  partition,  water  very  slightly,  but  keep  the  other  side  of  the  box 
well  soaked.  After  two  weeks,  take  up  some  of  the  seedlings  and  note  the 
effect  on  the  roots. 


Water  a  Factor  which  determines  the  Course  taken  by  Roots.  — 

Water,  as  well  as  the  force  of  gravity,  has  much  to  do  with  the  direction 

taken  by  roots.  Water  is 
always  found  below  the  sur- 
face of  the  ground,  but 
sometimes  at  a  great  depth. 
In  order  to  obtain  a  supply 
of  water,  the  roots  of  plants 
frequently  spread  out  for 
very  great  distances.  Most 
trees,  and  all  grasses,  have 
a  greater  area  of  surface 
exposed  by  the  roots  than 
by  the  branches.  The  mes- 
quite  bush,  a  low-growing 
tree  of  the  American  and 
Mexican  deserts,  often  sends 
roots  downwards  for  a  dis- 
tance of  forty  feet  after 
water.  The  roots  of  alfalfa, 
a  cloverlike  plant  used  for 
hay  in  the  Western  states, 
often  penetrate  the  soil  after  water  for  a  distance  of  ten  to  twenty 
feet  below  the  surface  of  the  ground. 

Structure  of  a  Taproot.  —  To  understand  fully  the  structure  of 
the  root,  it  will  be  necessary  for  us  to  examine  some  large,  fleshy 
root  (a  taproot),  so  that  we  may  get  a  little  first-hand  evidence  as 
to  its  internal  structure.  If  you  cut  open  a  parsnip  or  carrot  so  as 
to  make  a  cross  section  of  the  root,  you  find  two  distinct  areas  —  an 
outer  portion,  the  cortex,  and  an  inner  part,  the  wood.  If  you  cut 
another  parsnip  in  lengthwise  section,  these  structures  show  still 


Dandelion  plant.     Note  the  length  of  the  root 
Photographed  by  Overton. 


ROOTS  AND   THEIR  WORK 


87 


A  cross  section  through  a  taproot  (a 
parsnip) :  C,  cortex;  W,  wood.  Notice 
in  the  right-hand  specimen,  which 
has  been  dipped  in  iodine,  that  the 
core  of  wood  continues  out  into  the 
rootlets  which  leave  the  main  root. 
Where  is  most  starchy  food  stored  in 
a  parsnip? 


more  plainly.  An  additional  fact  is  seen;  namely,  that  all  the 
smaller  roots  leaving  the  main  or  primary  root  have  a  core  of  wood 
which  bores  its  way  out  through 
the  cortex  wherever  the  small 
rootlets  are  given  off. 

Fine  Structure  of  a  Root. — If 
we  could  now  examine  a  much 
smaller  and  more  delicate  root  in 
thin  longitudinal  section  under 
the  compound  microscope,  we 
should  find  the  entire  root  to 
be  made  up  of  cells,  the  walls 
of  which  are  uniformly  rather 
thin.  (Cross  sections  and  lon- 
gitudinal sections  of  tradescantia 
roots  are  excellent  for  demonstra- 
tion of  these  structures.)  Over 
the  lower  end  of  the  root  is 
found  a  collection  of  cells,  most  of  which  are  dead,  loosely  ar- 
ranged so  as  to  form  a  cap  over  the  growing  tip.  This  is 
evidently  an  adaptation  which  protects  the  young  and  actively 
growing  cells  just  under  the  root  cap.  In  the  body  of  the  root 
the  central  cylinder  can  easily  be  distinguished  from  the  surround- 
ing cortex.     The  cells  of  the  former  have  somewhat  thicker  walls. 

In  a  longitudinal  section  a  series  of 
tubelike  structures  may  be  found 
within  the  central  cylinder.  These 
structures  are  cells  which  have  grown 
together  at  the  small  end,  the  long 
axis  of  the  cells  running  the  length 
of  the  main  root.  In  their  develop- 
ment the  cells  mentioned  have  grown 
together  in  such  a  manner  as  to  lose  their  small  ends,  and  now  form 
continuous  hollow  tubes  with  rather  strong  walls.  Other  cells 
have  come  to  develop  greatly  thickened  walls ;  these  cells  give 
mechanical  support  to  the  tubelike  cells.  Collections  of  such  tubes 
and  supporting  woody  cells  together  make  up  what  is  known  as 
fibrovascidar  bundles. 


The  end  of  a  growing  root,  tipped 
and  protected  by  the  root  cap ; 
g,  the  growing  point.  (Consider- 
ably magnified.) 


88 


ROOTS  AND  THEIR  WORK 


Cross  section  of  a  young  taproot : 
o,  a,  root  hairs ;  h,  epidermis ;  c, 
cortex ;  d,  fibrovascular  cylinder  or 
wood. 


Root  Hairs.  —  Careful  examination  of  the  root  of  one  of  the  seed- 
hngs  of  mustard,  radish,  or  barley  grown  in  the  pocket  germinator 

shows  a  covering  of  tiny  fuzzy 
structures.  These  structures  are 
very  minute,  at  most  3  to  4  mm. 
in  length.  They  vary  in  length 
according  to  their  position  on  the 
root,  the  most  and  the  longest  root 
hairs  being  found  near  at  the  point 
marked  R.  H.  in  the  Figure.  These 
structures  are  outgrowths  of  the 
outer  layer  of  the  root  (the  epi- 
dermis), and  are  of  very  great  im- 
portance to  the  living  plant. 

Structure   of  a   Root  Hair.  —  A 
single  root  hair  examined  under  a 
compound  microscope  will  be  found 
to  be  a  long,  round  structure,  almost  colorless  in  appearance.     The 

wall,  which  is  very  flexible  and    thin,     

is  made  up  of  cellulose,  a  substance 
somewhat  Hke  wood  in  chemical  com- 
position, through  which  fluids  may  easily 
pass. 

If  we  had  a  very  high  power  of  the 
microscope  focused  upon  this  cellulose 
wall,  we  should  be  able  to  find  under 
it  another  structure,  far  more  delicate 
than  the  cell  wall.  This  is  called  the 
cell  membrane.  Clinging  close  to  the 
cell  membrane  is  the  protoplasm  of 
the  cell.  The  interior  of  the  root  hair 
is  more  or  less  filled  with  a  fluid  called 
cell  sap.  Forming  a  part  of  the  living 
protoplasm  of  the  root  hair,  sometimes 
in  the  hairlike  prolongation  and  some- 
times in  that  part  of  the  cell  which 
forms  the  epidermis,  is  found  a  nucleus.  The  protoplasm,  nucleus, 
and  cell  membrane  are  alive ;  all  the  rest  of  the  root  hair  is  dead 


^R.H. 


Young  embryo  of  corn,  show- 
ing root  hairs  (R.  H),  and 
growing  stem  (P.). 


ROOTS  AND   THEIR   WORK 


89 


material,  formed  by  the  activity  of  the  living  substance  of  the 
cell.     The  root  hair  is  a  living  plant  cell  with  a  wall  so  delicate  that 
water    and    mineral    sub- 
stances from  the  soil  can 
pass  through   it  into  the 
interior  of  the  root. 

How  the  Root  absorbs 
Water.  —  The  process  by 
which  the  root  hair  takes 
up  soil  water  can  better 
be  understood  if  we  make 
an  artificial  root  hair  large 
enough  to  be  easily  seen. 
An  egg  with  part  of  the 
outer  shell  removed  so  as 
neath  is  an  example. 


Diagram  of  a 
CS,  ceU  sapi 
A'^,  nucleus; 


root  hair:  CM,  cell  membrane; 
CW,  cell  wall ;  P,  protoplasm  ; 
S,  soil  particles. 


to  expose  the  soft  membrane  under- 
Better,  a  root  hair  may  be  made  in  the 
following  way:  Pour  some  soft  celloidin  into  a  tube  vial;  carefully 
revolve  the  vial  so  that  an  even  film  of  celloidin 
dries  on  the  inside  of  the  vial.  This  is  removed, 
filled  with  white  of  egg,  and  tied  over  the  end  of 
a  rubber  cork  in  which  a  glass  tube  has  previously 
})een  inserted.  When  placed  in  water,  it  gives  a 
very  accurate  picture  of  the  root  hair  at  work. 
After  a  short  time  water  begins  to  rise  in  the 
tube,  having  passed  through  the  film  of  cel- 
loidin. If  grape  sugar,  salt,  or  some  other  sub- 
stance which  will  dissolve  in  water  were  placed 
in  the  water  outside  the  artificial  root  hair,  it 
could  soon  be  proved  by  test  to  pass  through 
the  wall  and  into  the  liquid  inside. 

Osmosis.  —  To  explain  this  process  we  must 
remember  that  gases  and  liquids  of  different 
densities,  when  separated  by  a  membrane  (a 
dehcate  porous  lining  having  no  holes  visible  to 
the  highest  power  microscope  we  possess),  tend 
to  flow  toward  each  other  and  mingle,  the  greatest  flow  always 
being  in  the  direction  of  the  denser  medium.  The  process  by  which 
two  gases  or  fluidsj  separated  by  a  membrane j  pass  through  the  mem- 


An  artificial  root 
hair,  showing  os- 
mosis taking  place. 


90 


ROOTS   AND   THEIR   WORK 


brane  and  mingle  with  each  other  is  called  osmosis.^  The  method 
by  which  the  root  hairs  take  up  soil  water  is  exactly  the  same  pro- 
cess. It  is  by  osmosis.  The  white  of  the  egg  is  the  best  possible 
substitute  for  living  matter;  it  has,  indeed,  almost  the  same 
chemical  formula  as  protoplasm.  The  celloidin  membrane  sepa- 
rating the  egg  from  the  water  is  much  like  the  dehcate  membrane 
and  wall  which  separates  the  protoplasm  of  the  root  hair  from  the 
water  in  the  soil  surrounding  it.  The  fluid  in  the  root  hair  is 
denser  than  the  soil  water ;  hence  the  greater  flow  is  toward  the 
interior  of  the  root  hair. 

Passage  of  Soil  Water  within  the  Root.  —  We  have  already  seen 
that  in  an  exchange  of  fluids  by  osmosis  the  greater  flow  is  always 

toward  the  denser  fluid. 
Thus  it  is  that  the  root 
hairs  take  in  more  fluid 
than  they  give  up. 
The  cell  sap,  which 
partly  fills  the  interior 
of  the  root  hair,  is  a 
fluid  of  greater  density 
than  the  water  outside 
in  the  soil.  When  the 
root  hairs  become  filled 
with  water,  the  density 
of  the  cell  sap  is  less- 
ened, and  the  cells  of 
the  epidermis  are  thus 
in  a  position  to  pass 
along  their  supply  of 
water  to  the  cells  next 
to  them  and  nearer  to 
the  center  of  the  root. 
These  cells,  in  turn, 
becbme  less  dense  than  their  inside  neighbors,  and  so  the  transfer 
of  water  goes  on  until  the  water  at  last  reaches  the  central  cylinder. 
Here  it  is  passed  over  to  the  tubes  of  the  woody  bundles  and  started 

'  For  an   excellent  elementary  discussion  of  osmosis  see  Moore,  Physiology  of 
Man  and  other  Animals.    Heniy  Holt  and  Company. 


A  potato  osinuineter.  The  lower  end  of  the  potato 
was  cut  off  and  the  remainder  peeled  for  about  one 
third  of  its  length.  A  hole  was  bored  to  within 
three  fourths  of  an  inch  of  the  cut  end  ;  a  small  hole 
was  bored  at  the  side  of  the  potato.  In  the  latter 
was  inserted  a  small  L-shaped  tube,  the  lower  end 
being  vaselined  to  make  it  air-tight.  Sugar  was 
then  placed  in  the  hole  at  the  top  and  a  cork  inserted  ; 
water  was  poured  into  the  dish  below.  Within  two 
hours  the  water  had  risen  in  the  tube,  as  shown  in 
the  right-hand  Figure. 


ROOTS  AND  THEIR  WORK 


di 


up  the  stem.  The  pressure  created  by  this  process  of  osmosis  is 
sufficient  to  send  water  up  the  stem  to  a  distance,  in  some  plants, 
of  twenty-five  to  thirty  feet.  Cases  are  on  record  of  water  having 
been  raised  in  the  birch  a  distance  of  eighty-five  feet. 

Physiological  Importance  of  Osmosis,  —  It  is  not  an  exaggera- 
tion to  say  that  osmosis  is  a  process  not  only  of  great  importance 
to  a  plant,  but  to  an  animal  as  well.  Foods  are  digested  in  the  food 
tube  of  an  animal ;  that  is,  they  are  changed  into  a  soluble  form  so 
that  they  may  pass  through  the  walls  of  the  food  tube  and  become 
part  of  the  blood.  Without  the  process  of  osmosis  we  should  be 
unable  to  use  much  of  the  food  we  eat. 


Problem  XV.    A  study  of  some  of  the  relations  between  roots 
and  the  soil.    {Laboratory  Manual,  Prdb.  XV,) 
(a)  Origin  of  soil. 
{b)  Kinds  of  soil. 

(c)  Water-retaining  ability, 

(d)  Fertility  of  soils. 

(e)  Hoot  hmrs  and  soil, 

if)  Boot  tubercles  and>  crop  rotation. 

Composition  of  Soil.  —  If  we  examine  a  mass  of  ordinary  loam  care- 
fully, we  find  that  it  is  composed  of  numerous  particles  of  varying  size 
and  weight.  Between  these 
particles,  if  the  soil  is  not 
caked  and  hard  packed,  we  can 
find  tiny  spaces.  In  well-tilled 
soil  these  spaces  are  constantly 
being  formed  and  enlarged. 
They  allow  air  and  water  to 
penetrate  the  soil.  If  we  ex- 
amine soil  under  the  micro- 
scope, we  find  considerable 
water  clinging  to  the  soil  par- 
ticles and  forming  a  delicate 
film  around  each  particle.  In 
this  manner  most  of  the  water 
is  held  in  the  soil. 

How  Water  is  held  in  Soil.  —  To  understand  what  comes  in  with  the 
soil  water,  it  will  be  necessary  to  find  out  a  little  more  about  soil.  Sci- 
entists who  have  made  the  subject  of  the  composition  of  the  earth  a  study, 
tell  us  that  once  upon  a  tune  at  least  a  part  of  the  earth  was  molten. 


Inorganic  soil  is  being  formed  by  weathering. 


92 


ROOTS  AND  THETR  WORK 


Later,  it  cooled  into  solid  rock.     Soil  making  began  when  the  ice  and 
frost,  working  with  the  heat,  chipped  off  pieces  of  rock.     These  pieces  in 

time  became  ground  into 
fragments  by  action  of  ice, 
glaciers,  running  water, 
or  the  atmosphere.  This 
process  is  called  weather- 
ing. Weathering  is  largely 
a  process  of  oxidation. 
A  glance  at  almost  any 
crumbling  stones  will  con- 
vince you  of  this,  because 
of  the  yeUow  oxide  of  iron 
(rust)  disclosed.  So  by 
slow  degrees  this  earth 
became  covered  with  a 
coating  of  what  we  call 
inorganic  soil.  Later,  gen- 
eration after  generation  of 
tiny  plants  and  animals 
which  lived  in  the  soil 
died,  and  their  remains 
formed  the  first  organic 
materials  of  the  soil. 

You    are    all    familiar 
with    the    difference    be- 
tween  the   so-called   rich 
soil  and   poor   soil.     The 
dark  soil  simply  contains  more  dead  plant  and  animal  life,  which  forms 
the  portion  called  humus. 

Humus  contains  Organic  Matter.  —  It  is  an  easy  matter  to  prove  that 
black  soil  contains  organic  matter,  for  if  an  equal  weight  of  carefully 
dried  humus  and  soil  from  a  sandy  road  is  heated  red-hot  for  some  time 
and  then  re  weighed,  the  hu- 
mus will  be  found  to  have 
lost  considerably  in  weight, 
and  the  sandy  soil  to  have  lost 
very  little.  The  material  left 
after  heating  is  inorganic 
material,  the  organic  matter 
having  been  burned  out. 

Organic  soil  holds  water 
much  more  readily  than  in- 
organic soil,  as  a  glance  at 
the     accompanying     Figure 


This  picture  shows  how  the  forests  help  to  cover  the 
inorganic  soil  with  an  organic  coating. 


:J  tSH 


A  B  C  D 

Experiment  to  illustrate  the  kind  of  soil  which  best 
retains  water :  A,  gravel;  5,. sand;  C,  barren 
soil ;  D,  rich  soil ;  E,  leaf  mold ;  F,  dry  leaves. 


ROOTS  AND  THEIR  WORK  93 

shows.  If  we  fill  each  of  the  vessels  with  a  given  weight  (say  100  grams 
each)  of  gravel,  sand,  barren  soil,  rich  loam,  leaf  mold,  and  25  grams  of 
dry,  pulverized  leaves,  then  pour  equal  amounts  of  water  (100  c.c.)  on 
each  and  measure  all  that  runs  through,  the  water  that  has  been  retained 
will  represent  the  water  supply  that  plants  could  draw  on  from  such  soil. 

The  Root  Hairs  take  more  than  Water  out  of  the  Soil.  —  If  a 
root  containing  a  fringe  of  root  hairs  is  washed  off  carefully,  it  will 
be  found  to  have  little  particles  of  soil  still  clinging  to  it.  Exam- 
ined under  the  microscope,  these  particles  of  soil  seem  to  be  ce- 
mented to  the  sticky  surface  of  the  root  hair.  The  soil  contains, 
besides  a  number  of  chemical  compounds  of  various  mineral  sub- 
stances, — lime,  potash,  iron,  silica,  and  many  others,  —  a  consider- 
able amount  of  organic  material.  Acids  of  various  kinds  are  present  in 
the  soil — nitric  acid,  which  comes  from  the  dead  bodies  of  plants  and 
animals  as  they  decay  and  oxidize ;  carbonic  acid,  formed  by  the 
union  of  the  carbon  dioxide  from  the  roots  and  the  water  in  the 
soil,  and  other  acids.  These  acids  so  act  upon  certain  of  the 
mineral  substances  that  they  become  dissolved  in  the  water  which 
is  absorbed  by  the  root  hairs. 

The  proportion  of  each  of  these  mineral  materials  is  very  small 
compared  with  the  water  in  which  they  are  found.  A  very  great 
amount  of  water  must  be  taken  up  by  the  roots  in  order  that  the 
plant  may  get  the  needed  amount  of  mineral  matter  with  which  to 
build  its  protoplasm. 

Plants  will  not  grow  well  without  certain  of  these  mineral  sub- 
stances. This  can  be  proved  by  the  growth  of  seedlings  in  a  so- 
called  nutrient  solution.  Such  a  solution  contains  all  the  mineral 
matter  that  a  plant  uses  for  food.^  If  certain  ingredients  of  this 
solution  are  left  out  the  plants  placed  in  such  a  solution  will  not 
live. 

1  A  nutrient  solution  may  be  prepared  as  follows :  — 

Distilled  water  (H2O) 1000.00    c.c. 

Potassium  nitrate  (KNOs) 1.00    tjx&ux 

Sodium  chloride  (NaCl)  0.50    gram 

Calcium  sulphate  (CaS04) 0.50    gram 

Magnesium  sulphate  (MgS04) 0.50    gram 

Calcium  phosphate  (Ca3[P04]2) 0.50    gram 

Ferric  chloride  (FeClg) 0.005  gram 

(Do  not  put  the  ferric  chloride  into  the  solution  in  the  first  place,  but  add  a  drop 
of  it  to  each  bottle  when  the  seedlings  are  put  in.) 


94 


ROOTS  AND  THEIR  WORK 


Nitrogen  in  a  Usable  Form  necessary  for  Growth  of  Plants.  — • 
We  learned  that  humus  is  made  up  of  decayed  plant  and  animal 
bodies.  A  chemical  element  needed  by  the  plant  to  make  proto- 
plasm is  nitrogen.  This  element  cannot  be  taken  from  either  soil 
water  or  air  in  a  pure  state,  but  is  usually  obtained  from  the  organic 
matter  in  the  soil,  where  it  exists  with  other  substances  in  the  form 
of  nitrates.  Ammonia  and  other  organic  compounds  which  contain 
nitrogen  are  changed  by  two  groups  of  little  plants  called  hac- 
teria  which  oxidize  the  compounds,  first  into  nitrites  and  then 
nitrates,^ 

Relation  of  Bacteria  to  Free  Nitrogen. — It  has  been  known  since 
the  time  of  the  Romans  that  the  growth  of  clover,  peas,  beans, 

and  other  legumes  in  soil  causes 
that  ground  to  become  more  favor- 
able for  growth  of  other  plants. 
The  reason  for  this  has  been  dis- 
covered in  late  years.  On  the 
roots  of  the  plants  mentioned  are 
found  little  swellings  or  nodules; 
in  the  nodules  exist  millions  of 
bacteria,  which  take  out  nitrogen 
from  the  atmosphere  and  fix  it  so 
that  it  can  be  used  by  the  plant ; 
that  is,  they  form  nitrates  for  the 
plants  to  use.  Only  these  bac- 
teria, of  all  the  living  plants,  have 
the  power  to  take  the  free  nitrogen 
from  the  air  and  make  it  over  into 
a  form  that  can  be  used  by  the 
roots.  As  all  the  compounds  of 
nitrogen  are  used  over  and  over 
again,  first  by  plants,  then  as  food 
for  animals,  eventually  returning 
to  the  soil  again,  it  is  evident  that 
any  new  supply  of  usable  nitrogen  must  come  by  means  of  these 
nitrogen-fixing  bacteria. 

1  It  has  recently  been  discovered  that  under  some  conditions  these  bacteria  are 
preyed  upon  by  tiny  one-celled  animals  living  in  the  soil  and  are  so  reduced  in  num- 


Tubercles    containing    the  nitrogen- 
fixing  bacteria. 


ROOTS  AND  THEIR  WORK  95 

Rotation  of  Crops.  —  The  facts  mentioned  above  are  made  use 
of  by  careful  farmers  who  wish  to  make  as  much  as  possible  from  a 
given  area  of  ground  in  a  given  time.  Such  plants  as  are  hosts 
for  the  nitrogen-fixing  bacteria  are  planted  early  in  the  season. 
Later  these  plants  are  plowed  in  and  a  second  crop  is  planted. 
The  latter  grows  quickly  and  luxuriantly  because  of  the  nitrates 
left  in  the  soil  by  the  bacteria  which  lived  with  the  first  crop. 
For  this  reason,  clover  is  often  grown  on  land  in  which  it  is  pro- 
posed to  plant  corn,  the  nitrogen  left  in  the  soil  thus  giving 
nourishment  to  the  young  corn  plants.  This  is  known  as  rotation 
of  crops.  The  annual  yield  of  the  average  farm  may  be  greatly 
increased  by  this  means. 

Soil  Exhaustion  may  be  Prevented.  —  Besides  the  rotation  of 
crops,  other  methods  are  used  by  the  farmer  to  prevent  the  exhaus- 
tion of  raw  food  material  from  the  soil.  One  method  known  as 
fallowing  is  to  allow  the  soil  to  remain  idle  until  bacteria  and  oxida- 
tion have  renewed  the  chemical  materials  used  by  the  plants. 
This  is  an  expensive  method,  if  land  is  dear.  The  most  common 
method  of  enriching  soil  is  by  means  of  fertilizers,  material  rich  in 
plant  food.  Manure  is  most  frequently  used,  but  many  artificial 
fertilizers,  most  of  which  contain  nitrogen,  are  used,  because  they 
can  be  more  easily  transported  and  sold.  Such  are  ground  bone, 
guano  (bird  manure),  nitrate  of  potash,  and  many  others.  These 
contain  as  well  other  important  raw  food  materials  for  plants, 
especially  potash  and  phosphoric  acid.  Both  of  these  substances 
are  made  soluble  so  as  to  be  taken  into  the  roots  by  the  action 
of  the  carbon  dioxide  in  the  soil. 

Forms  of  Roots  and  their  Relation  to  the  Life  of  the  Plant.  —  Roots 
assume  various  forms.  The  form  or  position  of  the  root  is  usually  de- 
pendent on  the  needs  of  the  plant,  the  roots  acting  to  help  it  succeed  in 
certain  localities. 

Food  Storage  in  Roots  and  its  Economic  Importance.  —  The  use  to  the 
plant  of  the  food  stored  in  the  taproot  may  be  understood  if  we  take  up 
the  life  history  of  the  parsnip.  Such  a  plant  produces  no  seed  until  near 
the  end  of  the  second  year  of  its  existence,  its  growth  the  first  summer 
forming  the  root  we  use  as  food.     After  forming  seeds  the  plant  dies. 

bers  that  they  cannot  do  their  work  effectively.  If  then  the  soil  is  heated  artificially 
or  treated  with  antiseptics  so  as  to  kill  the  protozoa,  the  bacteria  which  escape 
multiply  so  rapidly  as  to  make  the  land  much  richer  than  before. 


ROOTS  AND   THEIR  WORK 


The  food  stored  in  its  root  enables  it  to  get  an  early  start  in  the  spring, 
so  as  to  be  better  able  to  produce  seeds  when  the  time  comes.  Such  plants 
live  only  under  rather  cool  climatic  conditions.  Examples  of  other  roots 
which  store  food  are  carrot,  radish,  yam,  sweet  potato,  etc.  This  food 
storage  in  roots  is  of  much  practical  value  to  mankind.  Many  of  our  com- 
monest garden  vegetables,  as  those  mentioned  above,  and  the  beet,  turnip, 
oyster  plant,  and  many  others  are  of  value  because  of  the  food  stored.  The 
sugar  beet  has,  in  Europe  especially,  become  the  basis  of  a  great  industry. 

Water  Roots.  —  In  the  duckweed,  a  plant  living  in  water,  the  roots 
are  short  and  contain  few  root  hairs.  The  water  supply  is  so  great  that 
few  root  hairs  have  been  called  forth.  The  water  hyacinth  is  another 
example  of  slight  development  of  roots.  The  plant  is  buoyed  up  by  the 
water  and  does  not  need  strong  roots  to  hold  it  firm. 

Adventitious  Roots.  —  Roots  are  often  developed  in  unusual  places. 
Roots  coming  out  thus,  as,  for  example, 
on  the  stem,  are  called  adventitious. 
Such  roots  are  developed  along  the 
stem  of  many  climbing  plants  —  for 
example,  the  roots  of  EngUsh  ivy. 

Some  plants,  as   strawberry,  couch 
grass,  and  many  others,  develop  new 


Couch  grass,  showing  how  the  plant  spreads 
by  striking  roots  from  a  reclining  stem. 


Corn  roots,  showing  prop  roots  de- 
veloped at  first  node  above  ground. 


plants  by  striking  root  at  any  point  on  the  reclining  stem  where  it  touches 
the  ground.  This  fact  is  made  use  of  by  practical  gardeners  in  the 
layering  of  plants. 

Examine  the  Indian  corn  for  another  kind  of  adventitious  roots.  Here 
they  serve  as  props  for  the  tall  stem.  In  the  young  seedlings  of  corn, 
notice  how  early  these  roots  develop.  Also  notice  the  manner  in  which 
they  arise  on  the  stem. 


ROOTS  AND  THEIR  WORK  97 

Air  Roots.  —  In  tropical  forests,  where  the  air  is  always  warm  and 
moist,  some  plants  have  come  to  live  above  the  soil  on  the  trunks  of  trees, 
or  in  other  places  where  they  can  get  a  favorable  foothold.  Such  plants 
are  called  epiphytes,  or  air  plants.  The  tropical  orchid  seen  in  our  green- 
houses is  an  example.  Examine  the  roots  of  such  a  plant.  Notice  how 
thick  they  are.  They  are  usually  provided  with  a  spongy  tissue  around 
the  outside  which  has  the  function  of  absorbing  water. 

Parasitic  Roots.  —  A  Jew  plants  live  on  other  living  plants,  and  develop 
by  the  aid  of  nourishment  taken  at  their  expense.  Such  a  plant  is  called  a 
parasite.  The  plant  or  animal  on  which  the  parasite  lives  is  called  the  host. 
The  mistletoe  is  an  example  of  a  parasitic  plant.  An  examination  of  its 
roots  shows  that  they  have  bored  their  way  into  the  stem  of  the  host. 
These  roots  not  only  penetrate  the  bark,  but  push  toward  the  center  of  the 
tree,  taking  nourishment  from  the  cells  there.  The  dodder  is  another 
seed-bearing  plant  which  has  this  habit.  Dodder  produces  from  seed,  but 
is  unable  to  live  alone  after  it  has  passed  the  seedling  stage,  and  will  die  if 
it  cannot  find  a  suitable  host.  It  is  found  on  many  common  weeds,  as 
jewel  weed  and  goldenrod.  Many  of  the  lower  plants  live  as  parasites, 
among  them  being  mildew,  rusts,  and  smuts  found  on  roses,  grain,  and 
corn. 

Reference  Books 

elementary 

Sharpe,  A  Laboratory  Manual  for  the  Solution  of  Problems  in  Biology.     American 

Book  Company. 
Andrews,  Botany  all  the  Year  Round,  Chap.  II.    American  Book  Company. 
Atkinson,  First  Studies  of  Plant  Life,  Chaps.  IX,  XI,  XII.     Ginn  and  Company. 
Coulter,  Plant  Studies,  Chap.  V.     D.  Appleton  and  Company. 
Goff  and  Mayne,  First  Principles  of  Agriculture.     American  Book  Company. 
Moore,  The  Physiology  of  Man  and  Other  Animals,  Henry  ITolt  and  Company. 
Stevens,  Introduction  to  Botany,  pages  31-44.     D.  C.  Heath  and  Company. 

ADVANCED 

Coulter,  Barnes,  and  Cowles,  A  Textbook  of  Botany,  Part  II.     American  Book  Com^ 

pany. 
Detmer-Moor,  Practical  Plant  Physiology.     The  Macmillan  Company. 
Goodale,  Physiological  Botany.     American  Book  Company. 
Gray,  Structural  Botany,  pages  27-39,   56-64.     American  Book  Company. 
Green,  Vegetable  Physiology,  Chaps.  V,  VI.     J.  and  A.  Churchill. 
Farmers'  Bulletin  86,  U.S.  Department  of  Agriculture. 
Kerner-Oliver,  Natural  History  of  Plants.     Henry  Holt  and  Company. 
MacDougal,  Plant  Physiology.    Longmans,  Green,  and  Company. 
Pfeffer,  W.,  The  Physiology  of  Plants.     Clarendon  Press. 


HUNT.    ES.    BIO. 


VIII.   THE  STRUCTURE  AND  WORK  OF  THE  STEM 


Problem  XVI.    Relationship  of  buds  to  the  growing  plant 
(optional).    (Laboratory  Manual,  Proh.  XVI.) 

Structure  of  a  Bud.  —  If  we 
cut  a  head  of  cabbage  through 
the  long  axis  of  its  stem,  we  find 
that  the  stem  is  much  shortened 
or  dwarfed,  and  that  the  leaves 
are  so  placed  as  to  cover  it  en- 
tirely. The  cabbage  is  a  big  bud. 
If  we  carry  out  our  definition  of  a 
bud,  starting  with  what  we  have 


A.  Cabbage  head  cut  lengthwise  to 
show  that  it  is  a  big  bud.  B.  The 
bud  under  favorable  conditions  has 
grown  into  an  elongated  stem. 


THE  STRUCTURE  AND   WORK   OF   THE  STEM     99 


seen  in  the  cabbage,  we  might  say  that  a  bud  is  a  very  much  shortened 
branch,  or,  in  reality,  "  the  promise  of  a  branch." 

Factors  which  influence  the  Opening  of  a  Bud.  —  A  bud  responds  to 
the  same  stimuli  that  we  have  seen  call  a  young  plant  into  active  life  from 
the  seed.  If  a  branch  containing  unopened  buds  (such  as  horse-chestnut 
or  willow)  is  placed  in  water  in  a  moderately  warm  room,  it  will  respond 
to  the  factors  without  it  and  begin  to  open.  The  tips  of  branches,  still 
attached  to  the  tree  outdoors,  may  be  introduced  into  a  warm  room 
through  a  hole  bored  in  the  window  sash.  They  will  open  to  bear  flowers 
and  leaves  during  the  coldest  months  of  the  year.  The  factors  which 
influence  the  germination  of  seeds  also  act  on  the  bud. 

Adaptations  in  the  Bud  of  Horse-Chestnut.  —  If  we  now  turn  our  at- 
tention to  horse-chestnut  buds  which  have  been  previously  placed  in 
water  to  open,  we  shall  be  able  to  get  some  notion  of  the  wonderful  adap- 
tations of  the  bud  which  fit  it  for  its  work. 

In  the  first  place,  a  horse-chestnut  bud  is  covered  with  a  sticky  ma- 
terial. Not  only  does  this  covering  keep  out  unwelcome  visitors  which 
might  bore  into  the  bud  and  destroy  the  tender  parts  within,  but  it  also 
serves  as  a  waterproof  cover- 
ing against  the  icy  rains  of 
the  late  fall  and  early  spring, 
and  against  evaporation  in 
dry  weather.  In  the  unopened 
buds  the  scales  overlap  like 
shingles  on  a  roof.  In  buds 
which  have  begun  to  open,  we 
find  that  not  only  have  the 
tiny  green  leaves  been  pro- 
tected by  the  outer  scales,  but 
they  have  been  additionally 
wrapped  in  soft,  cottony  sub- 
stance. The  young  leaves  are 
always  folded  or  rolled  up  in 
the  bud.  Two  purposes  are 
thus  served  —  protection  from 
the  elements  and  from  drying 
by  little  exposure  of  the  deli- 
cate surface,  and  economy  of 
space  by  means  of  the  tight 
and  compact  stowing  away  of 
the  parts  thus  folded. 

Why  Buds  are  Covered.  — 
When  we  consider  that  most  of  our  earliest  green  leaves  come  from  open- 
ing buds  in  the  early  spring,  the  importance  of  a  protective  covering  is 
well  seen.     Nevertheless,  buds  are  frozen  time  and  again  during  the  cold 


Opening  bud  of  horse-chestnut :  L.,  leaves ; 
L.S.,  leaf  scar;  S.,  scalelike  leaves  which 
cover  bud. 


100      THE  STRUCTURE  AND  WORK   OF   THE   STEM 


weather,  only  to  thaw  out  again  without  injury  to  the  plant.     Sudden 


changes,  however,  do  much  harm, 
winter  weather  when  temperature 
conditions  are  seemingly  favorable  ; 
a  definite  length  of  growth  seems 
in  that  case  to  be  necessary.  Dur- 
ing warm  weather  plants  give  rise 
to  buds  which  are  devoid  of  pro- 
tective scale  leaves.  Such  is  also 
noticed  in  tropical  forms,  which  are 
not  called  upon  to  meet  rigorous 
climatic  conditions. 

Position  of  the  Bud  on  the 
Stem.  —  The  growth  of  the  stem 
from  the  bud  can  best  be  observed 
in  a  very  young  seedling.  If,  for 
example,  we  examine  a  pea  seed- 
Ung,  it  will  be  seen  that  the  plumule 
or  epicotyl  is  the  first  bud  of  the 
plant.     It  produces  the  first  stem 


Some  buds  do  not  open  during  mild 


and  leaves.  Buds  come  out 
at  the  ends  of  branches 
{terminal)  and  at  the  sides 
{lateral). 

Deliquescent  Tree. — 
The  position  of  the  most 
active  buds  determines  the 
form  of  the  future  tree.  If 
you  examine  a  A\dnter  branch 
of  the  apple,  elm,  or  oak 
tree,  you  will  find  that  the 
lateral  buds  have  developed 
more  strongly  and  more  rapidly  than  the  terminal  bud.  Thus  the  tree  has 
come  to  assume  during  its  growth  a  rounded  shape  due  to  the  rather 
more  rapid  development  of  the  lateral  buds.  Such  a  tree,  having  a 
rather  stout,  short  trunk,  mth  many  low,  spreading,  lateral  branches, 
is  said  to  be  deliquescent. 


A  larch,  an  excurrent  tree  (at  right)  and  an  elm, 
a  deliquescent  tree  (at  left).  Photographed  by 
W.  C.  Barbour. 


THE  STRUCTURE  AND   WORK  OF  THE  STEM    101 


Excurrent  Tree.  —  If,  on  the  other  hand,  the  terminal  buds  of  the  tree 
get  a  better  supply  of  light,  food,  or  if  other  factors  aid  its  growth,  the 
tree  will  be  tall  and  have  but  one  main  trunk,  such  as  the  Lombardy 
poplar,  and  pines  and  cedars.  Such  a  tree  is  named  excurrent.  The 
picture  shows  trees  of  these  two  shapes. 

Problem  XVTI.  The  structure 
ami  work  of  stems.  {Laboratory 
Manual,  Prob.  XVII.) 

(a)  EMernal  structure  of  a  di- 
cotyledonous stem  {optional). 

(b)  Internal  structure  of  a  di- 
cotyledonous stem. 

(c)  Circulation  in  stems, 
id)    Condition  of  food   parsing 

through  the  stem,. 

The  External  Structure  of  a  Dicotyle- 
donous Stem.  — A  horse-chestnut  twig  in 
its  winter  condition  shows  the  structure 
and  position  of  the  buds  very  plainly. 
As  the  twig  grew  last  year  the  scales 
which  covered  the  outside  of  the  terminal 
bud  dropped  off,  and  the  young  shoot 
developed  from  the  opened  bud.  The 
scales  which  dropped  off  left  marks 
forming  a  little  ring  upon  the  surface  of 
the  twig.  These  rings,  collectively  named 
the  hud  scars,  enable  one  to  tell  the  age 
of  the  branch. 

Just  above  the  lateral  buds  are  marks, 
known  as  leaf  traces,  that  show  the  points 
at  which  leaves  were  attached.  A  care- 
ful inspection  of  the  leaf  traces  reveals 
certain  tiny  dotlike  scars  arranged  more 
or  less  in  the  form  of  a  horseshoe.  These 
scars  mark  the  former  position  of  bundles 
of  tubes  which  we  have  already  studied 

in  connection  with  roots.  They  are,  in  fact,  continuations  of  the  same 
fibrovascular  l>undles  which  pass  from  the  root  up  through  the  stem  and 
out  into  the  leaves,  where  we  see  them  as  the  veins  which  act  as  the 
support  of  the  soft  green  tissues  of  the  leaf.  The  most  important  use  to 
the  plant  of  the  fibrovascular  bundles  is  the  condvx^tion  of  fluids  from  the 


Throo-ycar-old  apple  branch, 
showing  terminal  and  lateral 
buds  and  bud  scars. 


102      THE   STRUCTURE  AND   WORK   OF   THE   STEM 

roots  to  the  leaves  and  jrotri  the  leaves  to  the  stem  and  root.  The  position  of 
the  leaf  traces  on  the  branch  give  us  a  clew  as  to  the  appearance  of  the 
leafy  tree.  If  the  leaf  traces  are  oppositely  placed,  then  we  know  that 
the  leaves  and  buds,  which  give  rise  to  lateral  branches,  had  a  very 
definite  arrangement  in  pairs.  Such  are  the  maple  or  horse-chestnut. 
If,  on  the  other  hand,  the  leaf  traces  are  placed  alternate  to  each  other, 
we  can  picture  a  tree  with  much  less  regularity  in  the  position  of  leaves 
and  lateral  branches,  as  in  the  apple,  beech,  and  elm. 


Four  years'  growth  in  an  ailanthus  stem,  showing  the  changes  in  the  lenticels  from 
round  holes  to  elongated  cracks  in  the  bark.  The  lenticel  in  a  young  shoot  is 
like  the  breathing  hole  of  a  leaf. 

Lenticels  and  their  Uses.  —  The  very  tiny  scars,  which  look  like  little 
cracks  in  the  bark,  are  very  important  organs,  especially  during  the  winter 
season,  for  they  are  the  breathing  holes  of  the  tree.  A  tree  is  alive  in 
winter,  although  it  is  much  more  active  in  the  warm  weather.  Oxidation 
takes  place  much  more  rapidly  in  the  summer  because  the  plant  is  grow- 
ing rapidly,  and  more  fuel  is  consumed  to  release  the  energy  needed  for 
growth.  We  shall  see  later  that  the  leaves  are  the  chief  breathing  organs 
of  the  plant.  But  all  the  year  round  oxygen  is  taken  in  and  carbon 
dioxide  given  off  through  the  lenticels,  as  the  breathing  holes  in  the  trunk 
and  branches  of  a  tree  are  called.  The  lenticels,  which  early  in  the  Ufe 
of  the  stem  are  structures  similar  to  the  breathing  holes  in  leaves  (of  which 
more  later) ,  become  quite  changed  in  older  stems,  the  tiny  holes  becoming 
cracklike  scars. 

A  Dicotyledonous  Stem  in  Cross  Section.  —  If  we  cut  a  cross  sec- 
tion through  a  young  horse-chestnut  stem,  we  find  it  shows  three 


THE  STRUCTURE  AND   WORK   OF   TUE   STEM     103 


Section  across  a  young  twig  of  box 
elder,  showing  the  four  stem  regions  : 
e,  epidermis,  represented  by  the 
heavy  bounding  line  ;  c,  cortex ;  to, 
wood;  p,  pith.  (From  Coulter, 
Plant  Relations.) 


distinct  regions.     The  center  is  occupied  by  the  spongy,  soft  pith; 

surrounding  this  is  found  the  rather  tough  wood,  while  the  outer- 
most area  is  called  cortex  or  bark. 

More  careful  study  of  the  bark 

reveals    the    presence    of    three 

layers  —  an  outer  layer,  a  middle 

green  layer,  and  an  inner  fibrous 

layer,  the  latter  usually  brown  in 

color.     This    layer   is    made   up 

largely   of    tough   fiberlike    cells 

known  as  bast  fibers.     The  most 

important    parts    of    this    inner 

bark,  so  far  as  the  plant  is  con- 
cerned, are  many  tubelike  struc- 
tures   known    as    sieve    tubes. 

These  are    long    rows  of    living 

cells,  having  perforated  sievelike 

ends.     Through  these  cells  food 

materials  pass  downward  from  the  upper  part  of  the  plant,  where 

they  are  manufactured. 
C  In  the  wood  will  be  noticed 

(see  Figure)  a  number  of  lines 
radiating  outward  from  the 
pith  toward  the  cortex.  These 
are  the  so-called  medullary 
rays,  thin  plates  of  pith  which 
separate  the  wood  into  a  num- 
ber of  wedge-shaped  masses. 
These  masses  of  wood  are 
composed  of  many  elongated 
cells,  which,  placed  end  to 
end,  form  thousands  of  little 
tubes  connecting  the  leaves 
with  the  roots.  In  addition 
to  these  are  many  thick-walled 
cells,  which  give  strength  to 
the  mass  of  wood.  In  sec- 
tions   of    wood    which    have 


Section  across  a  twig  of  box  elder  three 
years  old,  showing  three  annual  growth 
rings  in  the  vascular  cylinder.  The  ra- 
diating lines  (m),  which  cross  the  wood 
(w),  represent  the  pith  rays,  the  prin- 
cipal ones  extending  from  the  pith  to  the 
cortex  (c).  (From  Coulter,  Plant  Rela- 
tions.) 


104      THE   STRUCTURE  AND   WORK  OF   THE  STEM 

taken  several  years  to  grow,  we  find  so-called  annual  rings.  The 
distance  between  one  ring  and  the  next  (see  Figure)  usually  rep- 
resents the  amount  of  growth  in  one  year.  Growth  takes  place 
from  an  actively  dividing  layer  of  cells,  known  as  the  cambium 
layer.  This  layer  forms  wood  cells  from  its  inner  surface  and 
bark  from  its  outer  surface.  Thus  new  wood  is  formed  as  a  dis- 
tinct ring  around  the  old  wood. 

Use  of  the  Outer  Bark.  —  The  outer  bark  of  a  tree  is  protective. 
The  cells  are  dead,  the  heavy  woody  skeletons  serving  to  keep  out 


Experiment  to  show  that  the  skin  of  the  i)()tat()  (:i  .stem)  retards  evaporation. 


cold  and  dryness,  as  well  as  prevent  the  evaporation  of  fluids  from 
within.  Most  trees  are  provided  with  a  layer  of  corky  cells.  This 
layer  in  the  cork  oak  is  thick  enough  to  be  of  commercial  impor- 
tance. The  function  of  the  corky  layer  in  preventing  evaporation 
is  well  seen  in  the  case  of  the  potato,  which  is  a  true  stem,  though 
found  underground.  If  two  potatoes  of  equal  weight  are  balanced 
on  the  scales,  the  skin  having  been  peeled  from  one,  the  peeled  po- 
tato will  be  found  to  lose  weight  rapidly.  This  is  due  to  loss  of 
water,  which  is  held  in  by  the  skin  of  the  unpeeled  potato. 

Passage  of  Fluids  up  and  down  the  Stem. — If  any  young  grow- 
ing shoots  (young  seedlings  of  corn  or  pea,  or  the  older  stems  of 
garden  balsam,  touch-me-not,  or  sunflower)  are  placed  in  red  ink 


THE  STRUCTURE  AND   WORK  OF    THE   STEM    105 


Apple  twigs  split  to  show  the 
course  of  colored  water  up 
the  stem. 


(eosin),  left  in  the  sun  for  a  few  hours,  and  then  examined,  the  red 
ink  will  be  found  to  have  passed  up  the  stem.  If  such  stems  were 
examined  carefully,  it  would  be  seen  that 
the  colored  fluid  is  confined  to  the  collec- 
tions of  woody  tubes  inamediately  under 
the  inner  bark.  Water  evidently  rises  in 
that  part  of  the  stem  we  call  the  wood. 

But  if  willow  twigs  are  placed  in  water 
roots  soon  begin  to  develop  from  that 
part  of  the  stem  which  is  under  water. 
If  now  the  stem  is  girdled  by  removing 
the  bark  in  a  ring  just  above  where  the 
roots  are  growing,  the  latter  will  even- 
tually die,  and  new  roots  will  appear 
alx)ve  the  girdled  area.  The  food  ma- 
terial necessary  for  the  outgrowth  of 
roots  evidently  comes  from  above,  and 
the  passage  of  food  materials  takes  place 
in  a  downward  direction  just  outside 
the  wood  in  the  layer  of  bark  which  contains  the  bast  fibers  and 
sieve  tubes.  Food  substances  are  also  conducted  to  a  much  less 
extent  in  the  wood  itself,  and  food  passes  from  the  inner  bark  to 
the  center  of  the  tree  by  way  of  the  pith  plates  or  medullary 
rays.  This  can  be  proved  by  testing  for  starch  in  the  medullary 
rays  of  young  stems.  It  is  found  that  much  starch  is  stored  in 
this  part  of  the  tree  trunk.  This  experiment  with  the  willow 
explains  why  it  is  that  trees  die  when  girdled  so  as  to  cut  the 
sieve  tubes  of  the  inner  bark.  The  food  supply  is  cut  off  from 
the  protoplasm  of  the  cells  in  the  part  of  the  tree  below  the  cut 
area.  Many  of  the  canoe  birches  of  our  Adirondack  forest  are 
thus  killed,  girdled  by  thoughtless  visitors. 

In  What  Form  does  Food  pass  through  the  Stem?  —  We  have 
already  seen  that  materials  in  solution  (those  substances  which  will 
dissolve  in  the  water)  will  pass  from  cell  to  cell  by  the  process  of 
osmosis.  This  is  shown  in  the  experiment  illustrated  on  the 
iollowing  page.  Two  thistle  tubes  were  partly  filled,  one  with 
starch  and  water,  the  other  with  sugar  and  water,  and  a  piece 
of  parchment  paper  was  tied  over  the  end  of  each.    The  lower 


106      THE  STRUCTURE  AND  WORK   OF  THE  STEM 


Experiment  showing  the  osmosis  of 
sugar  (right-hand  tube)  and  non- 
osmosis  of  starch  (left-hand  tube). 


end  of  both  tubes  was  placed  in  a  glass  dish  under  water.     After 
twenty-four  hours,  the  water  in  the  dish  was  tested  for  starch, 

and  then  for  sugar.  We  find  that 
only  the  sugar,  which  has  been 
dissolved  by  the  water,  can  pass 
through  the  membrane. 

Digestion.  —  As  we  shall  see 
later,  the  food  for  a  plant  is  manu- 
factured in  the  leaves  or  in  stems, 
etc.,  wherever  green  coloring  mat- 
ter is  found.  Much  of  this  food 
is  in  the  form  of  starch.  But 
starch,  being  insoluble,  cannot  be 
passed  from  cell  to  cell  in  a  plant. 
It  must  be  changed  to  a  soluble 
form.  This  is  accomplished  by 
the  process  of  digestion.  We 
have  already  seen  that  starch  was 
changed  to  grape  sugar  in  the  corn  by  the  action  of  a  substance  (a 
digestive  ferment)  called  diastase.  This  process  of  digestion  seem- 
ingly may  take  place  in  all  living  parts  of  the  plant,  although  most 
of  it  is  done  in  the  leaves.  In  the  bodies  of  all  animals,  including 
man,  starchy  foods  are  changed  in  a  similar  manner,  but  by  other 
digestive  ferments,  into  soluble  grape  sugar.  (See  experiment, 
page  72.) 

The  food  material  may  be  passed  in  a  soluble  form  until  it  comes 
to  a  place  where  food  storage  is  to  take  place,  then  it  can  be  trans- 
formed to  an  insoluble  form  (starch,  for  example) ;  later,  when 
needed  by  the  plant  in  growth,  it  may  again  be  transformed  and  sent 
in  a  soluble  form  through  the  stem  to  the  place  where  it  will  be  used. 
Building  of  Proteids.  —  Another  very  important  food  substance 
stored  in  the  stem  is  proteid.  Of  the  building  of  proteid,  little  is 
known.  We  know  it  is  an  extremely  complex  chemical  substance 
which  is  made  in  plants  from  compounds  containing  nitrogen,  the 
nitrates  and  compounds  of  ammonia  received  through  the  roots 
from  the  organic  matter  contained  in  the  soil,  combined  with  sugar 
or  starches  in  the  body  of  the  plant. 
Some  forms  of  proteid  substance  are  soluble  and  others  insoluble 


THE  STRUCTURE  AND   WORK  OF  THE  STEM    107 

in  water.  White  of  egg,  for  example,  is  very  slightly  soluble,  but  can 
be  rendered  insoluble  by  heating  it  so  that  it  coagulates.  Insoluble 
proteids  are  digested  within  the  plant;  how  and  where  is  but  slightly 
understood.  In  a  plant,  soluble  proteids  pass  down  the  sieve  tubes 
in  the  bast  and  then  may  be  stored  in  the  bast  or  medullary  rays 
of  the  wood  in  an  insoluble  form,  or  they  may  pass  into  the  fruit  or 
seeds  of  a  plant,  and  be  stored  there. 


What  forces  Water  up  the  Stem.  —  We  have  seen  that  the  process  of 
osmosis  is  responsible  for  taking  in  soil  water,  and  that  the  enormous  ab- 
sorbing surface  exposed  by  the  root  hairs 
makes  possible  the  absorption  of  a  large 
amount  of  water.  Frequently  this  is  more 
than  the  weight  of  the  plant  in  every  twenty- 
four  hours. 

Experiments  have  been  made  which  show 
that  at  certain  times  in  the  year  this  water 
is  in  some  way  forced  up  the  tiny  tubes  of 
the  stem.  During  the  spring  season,  in 
young  and  rapidly  growing  trees,  water  has 
been  proved  to  rise  to  a  height  of  nearly 
ninety  feet.  The  force  that  causes  this  rise  of 
water  in  stems  is  known  as  root  pressure. 

But  root  pressure  alone  cannot  account 
for  the  rise  of  sap  (water  containing  materials 
taken  out  of  the  soil)  to  a  height  of  several 
hundred  feet,  as  in  the  stems  of  the  California 
big  trees.  Other  forces  must  play  a  part  here. 
One  way  in  which  the  rise  of  water  can  be 
partly  accounted  for  is  in  the  fact  that  capil- 
lary attraction  may  help  in  part.  If  you  place 
in  a  glass  containing  red  or  other  colored  fluid  three  or  four  tubes  of  differ- 
ent inside  diameter,  the  fluid  will  be  found  to  rise  very  much  higher  in  the 
tubes  having  a  smaller  diameter.  This  is  caused  by  capillarity  or  capil- 
lary attraction.  When  we  consider  that  the  tubes  in  the  stem  are  very  much 
smaller  than  any  we  can  make  out  of  glass,  it  can  be  seen  that  water 
jnight  rise  in  the  stem  to  some  height  in  tubes  of  microscopic  diameter. 

The  greatest  factor,  however,  is  one  which  will  be  more  fully  explained 
when  we  study  the  work  of  the  leaf.  Leaves  pass  off  an  immense  quan- 
tity of  water  by  evaporating  it  in  the  form  of  vapor.  This  evaporation 
seems  to  result  in  a  kind  of  suction  on  the  column  of  water  in  the  stem. 
In  the  fall,  after  the  leaves  have  gone,  much  less  water  is  taken  in  by 
roots,  showing  that  an  intimate  relation  exists  between  the  leaves  and 
the  root. 


Diagram  to  show  the  areas  in 
a  plant  through  which  raw 
food  materials  pass  up  the 
stem  and  food  materials 
pass  down.  (After  Stevens.) 


108      THE  STRUCTURE  AND  WORK   OF  THE  STEM 


Structure  of  a  Monocotyledonous  Stem.  —  A  piece  of  cornstalk  ex- 
amined carefully  in  cross  and  longitudinal  section  shows  us  that  the  main 
bulk  of  the  stalk  is  made  up  of  pith,  while  scat- 
tered through  the  pith  are  numerous  stringy,  tough 
structures.  To  these  the  name  fibrovascular  bundles 
has  been  given.  The  latter  are  the  woody  bundles 
of  tubes  which  in  this  stem  are  scattered  through 
the  pith  and  run  into  the  leaves  at  the  nodes, 
where  (in  young  specimens)  they  may  be  followed 
as  veins.  The  outside  of  the  corn  stem  is  formed 
of  large  numbers  of  these  bundles,  which,  closely 
packed  together,  form  an  outer  rind.  Thus  the 
woody  material  gives  mechanical  support  to  an 
otherwise  spongy  stem. 

Structure  of  Fibrovascular  Bundle  in  a  Mono- 
cotyledonous Stem.  —  A  fibrovascular  bundle  in 
a  cross  section  under  the  microscope  shows  this 
arrangement:  Around  the  outside  of  the  bundle 
is  a  collection  of  thick-walled,  woody  cells. 
These  cells  serve  to  support  the  bundle.  Inside 
of  these  cells  are  found  a  number  of  tubes  of 
different  diameters,  some  for  conduction  of  water, 
others  for  air,  and  still  others  for  liquid  food 
material  sent  down  from  the  leaves.  These 
tubes  were  formed  by  the  elongation  of  certain 
cells  of  the  bundle  which  in  their  growth  have 
divided  so  as  to 
form  a  string  of 
cells.  The  con- 
tents of  some  of 
these    cells  die: 


Longitudinal  section  of 
cornstalk,  showing 
some  of  the  fibrovas- 
cular bundles  passing 
outward  at  the  node 
just  above  the  roots. 


a  hollow  tube' of  cellulose  remains,  which 
admits  the  passage  of  material  from  one 
level  of  the  stem  to  another  through  the 
open  ends  of  the  cells.  The  conducting 
tubes  have  various  functions.  Some 
carry  soil  water  and  air  up  the  stem, 
while  others  take  food  material  down 
toward  the  roots.  The  bundles  elon- 
gate rapidly,  but  are  limited  in  their 
growth  outward  by  the  hard-walled, 
woody  cells.  An  old  stem  of  a  mono- 
cotyledon contains  more  bundles  than 
does  a  young  stem,  the  bundles  growing 
out  as  veins  into  the  leaves. 


Monocotyledonous  fibrovascular 
bundle  :  ph,  region  in  which  food 
passes  down  ;  d,  woody  portion 
or  bundle  ducts  which  carry  air 
and  water ;  p,  pith  cell. 


THE  STRUCTURE  AND   WORK   OF   THE   STEM     109 

Food  Storage.  —  Many  monocotyledonous  trees  which  Uve  for 
long  periods  of  time  store  food  in  large  quantities  in  the  trunk.  The 
sago  palm  is  an  example. 
The  sugar  cane  is  a  mono- 
cotyledonous stem  of  great 
commercial  value  because 
of  the  sugar  contained  in 
its  sap.  Over  70  pounds 
of  sugar  on  the  average  is 
used  annually  by  each  per- 
son in  the  United  States. 
Most  of  the  cane  sugar 
grown  in  this  country 
comes  from  Louisiana  and 
Texas,  although  these 
states  do  not  begin  to 
supply  the  needs  of  this 
country.  The  diagram  fol- 
lowing graphically  shows 
the  sources  and  kinds  of 
sugars  used  in  the  United 
States. 

Roots  and  Stems  as 
Food.  —  Underground 
stems  and  roots  form 
some  of  the  most  important  sources  of  man's  food  supply.  Our 
commonest  foods,  as  the  potato,  sweet  potato,  onion,  carrot,  parsnip, 
turnip,  and  beet,  are  well-known  examples.     The  sago  palm  is  the 

Kind  and  Sources  Sugar  Consumed  in  United  States — Percentage 

1,0  20  ^  10  'p  7jD aO BO 


Palms  and  palmettos;   typical  monocotyledo- 
nous plants.    Scene  on  Indian  River,  Florida. 


Beet 


East  Indies 


United  States 


Cuba 


Germany      Rest  World 


chief  support  of  many  of  the  natives  of  Africa.  Each  adult  tree  will 
furnish  700  pounds  of  sago  meal,  2i  pounds  being  enough  to  support 
a  man  one  day.  The  cassava  root,  from  which  tapioca  is  made,  is 
one  of  the  main  supports  of  African  natives.     Sugar,  from  the  beet 


no    THE  STRUCTURE  AND  WORK  OF  THE  STEM 

root,  is  a  world-known  commodity,  beet-sugar  production  having 
greatly  increased  in  recent  years.  Maple  sugar  is  a  well-known 
commodity  which  is  obtained  by  boiling  the  sap  of  sugar  maple 
until  it  crystallizes.  Over  16,000  tons  of  maple  sugar  is  obtained 
every  spring,  Vermont  producing  about  40  per  cent  of  the  total 
output. 

The  following  table  shows  the  proportion  of  foods  in  some  of  the 
commoner  roots  and  stems  :  — 


Water 


Proteids 


Carbohy- 
drates 


Fats 


Ash 


Potato  .  .  . 
Carrot  .  .  . 
Parsnip  .  .  . 
Turnip  .  .  . 
Onion  .  .  . 
^Sweet  potato  . 
Beet  .... 


75 

89 

81 

92.8 

91 

74 

82.2 


1.2 
.5 

1.2 
.5 

1.5 

1.5 
.4 


18 
5 

8.7 

4.0 

4.8 

20.2 

13.4 


0.3 
0.2 
1.5 
0.1 
0.2 
0.1 
0.1 


1.0 
1.0 
1.0 
.8 
.5 
1.5 
0.9 


Budding.  —  We  have  said  a  bud  is  a  promise  of  a  branch ;  it 
may  be  more,  the  promise  of  a  new  tree.  If  the  owner  of  an  apple 
or  peach  tree  wishes  to  vary  the  quaUty  of  fruit  borne  by  the  tree, 
he  may  in  the  early  fall  cut  a  T-shaped  incision  in  the  bark  and  then 
insert  a  bud  sur- 
rounded with  a 
little  bark  from 
the  tree  bearing 
the  desired  fruit.^ 
The  bud  is  bound 
in  place  and  left 
over  the  winter. 
When  a  shoot 
from  the  embed- 
ded bud  grows 
out  the    follow- 


I 


h 


Steps  in  Budding. 


1  This  bud  should 
be  taken  from  a  tree 
of  the  same  species. 


(a)  twig  having  suitable  buds  to  use  ;  (6)  method  of  cutting 
out  bud  ;  (c)  how  the  bark  is  cut ;  (d)  how  the  bark  is 
opened  ;  (e)  inserting  the  bud  ;  (/)  the  bud  in  place ; 
(g)  the  bud  properly  bound  in  place. 


THE   STRUCTURE  AND   WORK   OF   THE   STExM     111 


Steps  in  tongue  grafting. 


ing  spring,  it  is  found  to  have  all  the  characters  of  the  tree  from 
which  it  was  taken.     This  process  is  known  as  budding. 

Grafting.  —  Of  much  the  same  nature 
is  grafting.  Here,  however,  a  small 
portion  of  the  stem  of  the  closely  allied 
tree  is  fastened  into  the  trunk  of  the 
growing  tree  in  such  a  manner  that  the 
two  cut  cambium  layers  will  coincide. 
This  will  allow  of  the  passage  of  food 
into  the  grafted  part  and  insure  the 
ultimate  growth  of  the  twig.  Grafting 
and  budding  are  of  considerable  eco-  („)   the  two  branches  to  be 

nomic   value  to   the   fruit   grower,    as   it       joined  :    (6)   a  tongue  cut  in 

enables  him  to   produce  at  wiU  trees     ^^f^'  (c)  how  fitted  together ; 

,         .  ,     .  .   ^.  /.  r     -x  1  (d)  method  of  wrapping. 

bearmg  choice  varieties  of  frmt. 

In  both  of  the  above  processes,  the  secret  of  successful  growth 
lies  in  the  fact  that  the  cambium  surface  of  the  bud  or  the  graft 
comes  in  contact  with  the  cambium  of  the  tree  to  which  they  are 
applied,  thus  putting  them  in  direct  communication  with  a  supply 
of  food  from  the  already  established  tree. 

Modified  Stems.  —  We  have  aeen  in  previous  experiments,  external 
forces  may  act  on  the  organs  of  a  plant  so  as  to  change  its  appearance 

and  often  its  form  and  habit.  A  stem 
grown  in  complete  darkness  is  white 
instead  of  green.  The  bleaching  of  the 
celery  stems  by  covering  them  is  a 
familiar  example  of  this.  Thus,  in  na- 
ture, forces  which  we  know  of  as  light, 
gravity,  heat,  moisture,  wind,  and  per- 
haps other  factors,  influence  the  plant 
in  its  growth.  Thus  changes  may  take 
place  which  fit  or  adapt  the  parts  of  a 
plant  better  for  life  under  certain  con- 
ditions in  which  it  must  exist. 

Stems  modified  for  Water  or  Food 

Storage.  —  Many     stems     store    large 

quantities  of  food.     The  sago  palm  is 

an  example  of  such  a  stem.     In  most  woody  stems  food  is  stored  during 

some  parts  of  the  year  and  is  used  as  the  plant  comes  to  need  it.     In 

*  For  full  directions  for  budding  and  grafting,  see  Goff  and  Mayne,  First  Princi- 
ples of  Agriculture,  Chap.  XIX,  or  Hodge,  Nature  Study  and  Life,  pages  16&-179. 


The  ix)tat()  tuber  a  stem  ;  note  the 
branches  growing  from  the  "eyes" 
at  one  end. 


112      THE   STRUCTURE  AND   WORK   OF  THE  STEM 


other  stems  the  conditions  of  life  are  such  that  the  plant  has  come  to 
store  water  in  the  stem.  The  cactus,  which  we  shall  examine  more  in 
detail  later,  is  a  plant  that  has  developed  the  stem  for  the  storage  of 
water,  and  is  so  adapted  to  desert  conditions  as  to  prevent  the  evapora- 
tion of  water  from  the  plant. 

The  potato  tuber  is  simply  a  much  thickened  storage  stem,  as  one  may 
easily  prove  by  examination  of  the  so-called  "eyes"  of  a  sprouting  po- 
tato.    The  tiny  projection  growing  within  the  eye  is  a  bud,  which  may 

give  rise  to  a  branch  later.     Food  and  water 
are  stored  with  the  tuber. 

Underground  Stems  ;  the  Rootstock.  — 
Other  stems  not  only  contain  stored  food, 
but  run  underground  for  the  protection  of 
the  plant.  Such  a  stem 
is  the  rootstock  of  the  iris. 
Some  underground  stems 
do  not  store  food,  but 
grow  with  considerable 
rapidity,  thus  covering 
ground  and  starting  new 
outposts  of  the  plant  at  a 
distance  from  the  original 
plants.  The  pest  called 
quick  grass  or  couch 
grass,  found  in  almost 
every  lawn,  has  such  a 
stem.  It  may  be  cut  in 
pieces,  but  each  piece 
may  strike  root,  thus 
multiplying  the  plant. 
Bulbs.  —  In  the  bulb 
of  a  lily  or  the  onion  the  stem  is  covered  with  thickened 
leaves,  the  whole  making  a  compact  and  reduced  plant 
which,  because  of  its  storad  food,  enables  the  plant  to 
make  an  early  start  in  the  spring. 

Reduced  Stems.  —  In  some  plants  the  stem  is  so  re- 
duced as  to  be  almost  lost. '  This  may  be  of  a  distinct 
advantage  to  the  plant  in  enabling  it  to  escape  destruc- 
tion from  enemies.  Such  a  plant  is  the  common  dan- 
delion, which,  because  of  its  short  stem,  escapes  grazing 
animals  and  the  knives  of  lawn  mowers.  Many  other 
low-lying  weeds  are  partly  immune  from  dangers  which 
beset  taller  plants. 

Climbing  Stems.  —  Stems  may  twist  around  an  object  in  order  to  climb. 
Such  a  plant  is  the  morning-glory.     Here  the  stimulus  which  draws  tho 


Longitudinal  section  of  a  lily 
bulb.  Note  the  much  thick- 
ened leaves,  and  the  flower 
cluster  at  the  center.  Pho- 
tographed by  Overton. 


Catbrier ;  the  ten- 
drils  {T)  are 
modified  sti- 
pules (parts  of 
leaves)  ;  Th, 
thorn. 


THE  STRUCTURE   AND   WORK   OF  THE   STEM     113 


plant  upward  is  evidently  the  sun.  In  stems  which  make  use  of  this 
method  of  climbing,  it  is  noticed  that  each  stem  twines  around  the  sui>- 
port  in  a  given  direction,  some  revolving  with  the  course  of  the  sun, 
others  in  the  opposite  direction.  When  such  a  stem  touches  an  object 
during  its  first  growth,  it  is  im- 
mediately stimulated  to  turn 
toward  the  object  and  coil  around 
it. 

Leaves  and  Stems  modified  as 
Holdfasts.  —  In  the  common  nas- 
turtium (tropceolum)  the  leaves 
revolve  in  much  the  same  man- 
ner as  do  the  stems  mentioned 
above.  This  movement  results 
in  some  of  the  leafstalks  fasten- 
ing around  supports,  thus  draw- 
ing the  stem  up. 

Tendrils.  —  In  some  plants 
definite  climbing  organs,  known 
as  tendrils,  are  developed.  A 
tendril,  which  has  the  appear- 
ance of  a  much  twisted  stem, 
may  be  modified  from  part  of  a 
leaf,  as  an  entire  leaf,  or  as  part 
of  a  branch.  Tendrils  have  the 
habit  of  at  first  stretching  out  as 
far  from  the  main  stem  as  pos- 
sible, then  slowly  revolving. 
After  a  support  is  touched  they 
immediately  coil  around  it  and 
then  begin  to  curl  up  somewhat 
after  the  manner  of  a  watch 
spring.  This  draws  up  the  stem 
of  which  they  arc  a  part  to  the  support. 

Stems  modified  as  Thorns.  —  Leaves  h.nd  parts  of  leaves  may  be 
changed  into  thorns  for  the  protection  of  the  plant.  In  some  instances 
the  stem  becomes  a  spine  or  thorn.     Such  is  the  case  in  the  honey  locust. 

In  the  case  of  the  black  locust,  a  part  of  the  leaf,  the  stipule,  becomes 
the  thorn.  All  such  modifications  seem  to  result  in  the  better  protection 
of  tender  parts  which  might  otherwise  suffer  from  the  attack  of  brows- 
ing animals. 


A  honey   locutit 


;     the  thorns  are 
branches. 


modified 


HUNT. 


8. 


114      THE   STRUCTURE  AND   WORK   OF   THE  STEM 


Reference  Books 
elementary 

Sharpe,  A  Laboratory  Marmal  jor  the  Solution  of  Problems  in  Biology.    American 

Book  Company. 
Andrews,  Botany  All  the  Year  Round,  Chaps.  VI,  VII.     American  Book  Company. 
Atkinson,  First  Studies  of  Plant  Life,  Chaps.  IV,  V,  VI,  VIII,  XXI.     Ginn  and 

Company. 
Dana,  Plants  and  their  Children,  pages  99-129.     American  Book  Company. 
Goff  and  Mayne,  First  Principles  of  Agriculture.     American  Book  Company. 
Hodge,  Nature  Study  and  Life,  Chaps.  IX,  X,  XI.     Ginn  and  Company. 
Hunter  and  Valentine,  Laboratory  Manual  of  Biology.     Henry  Holt  and  Company. 
MacDougal,  The  Nature  and  Work  of  Plants.     The  Macmillan  Company. 

ADVANCED 

Apgar,  Trees  of  the  United  States,  Chaps.  II,  V,  VI.    American  Book  Company. 

Coulter,  Barnes,  and  Cowles,  A  Textbook  of  Botany,  Vol.  I.  American  Book  Com- 
pany. 

Ganong,  The  Teaching  Botanist.    The  Macmillan  Company. 

Goebel,  Organography  of  Plants,  Part  V.     Clarendon  Press. 

Goodale,  Physiological  Botany.    American  Book  Company. 

Gray,  Structural  Botany,  Chap.  V.     American  Book  Company. 

Kerner-Oliver,  Natural  History  of  Plants.     Henry  Holt  and  Company. 

Lubbock,  Buds  and  Stipules.     D.  Appleton  and  Company. 

Strasburger,  Noll,  Schenck,  and  Schimper,  A  Textbook  of  Botany.  The  Macmillan 
Company. 

Ward,  The  Oak.     D.  Appleton  and  Company. 

Yearbook,  U.S.  Department  of  Agriculture,  1894,  1895,  1898-1910. 


IX.   LEAVES  AND  THEIR  WORK 

Problem  XVIII.    A   study  of  leaves  in  relation  to  their 
enviromnent,    {Ldboratory  Manual,  Prob.  XVIII.) 
(a)  Reactions  of  stems  and  leaves  to  light. 
(jb)  Structure. 
(c)  Important  functions. 

{!)  Absorption  and  respiration. 

(^)  Food-making  and  its  by-product. 

(5)  Evaporation  of  excess  waler. 

(4)  TJie  leaf  as  a  mill  {optional), 
(jd)  Means  of  protection  {optional). 
(e)  Som£>  leaf  modifications  {optional). 
(/)  Importance  to  man. 


Differences  between  Roots  and  Stems.  —  A  comparison  of  the 
young  root  and  developing  stem  of  a  bean  seedling  show  that  sev- 
eral marked  differences  exist :  (1)  the  color  of  the  stem  is  greenish, 
while  the  roots  are  gray  or  whitish ;  (2)  the  stem  has  leaves  and 
branches  leaving  it  in  a  more  or  less  regular  manner,  while  the 
smaller  roots  are  extremely  irregular  in  their  method  of  growth ; 
(3)  the  stem  grows  up- 
ward, while  the  general 
direction  taken  by  the 
roots  is  downward. 

Effect  of  Light  on  Plants. 
— In  young  plants  which 
have  been  grown  in  total 
darkness,  no  green  color  is 
found  in  either  stems  or 
leaves,  the  latter  often 
being  reduced  to  mere 
scales.       The    stems    are 

,  J  ,  A  pocket  garden  which  has  been  kept  in  com- 

long  and  more  or  less  re-  pj^^e  darkness  for  several  weeks.     Notice  the 

dining.      We   can   explain  bleached  condition  of  stems  and  leaves. 

115 


1 

■ 

1 

116 


LEAVES  AND   THEIR  WORK 


the  changed  condition  of  the  seedUng  grown  in  the  dark  only  by 
assuming  that  hght  has  some  effect  on  the  protoplasm  of  the 
seedling  and  induces  the  growth  of  the  green  part  of  the  plant. 
Numerous  instances  could  be  given  in  which   plants  grown  in 

sunlight  are  healthier  and 
better  developed  as  to 
their  green  parts  than 
those  in  the  shady  parts  of 
a  garden  or  field.  On  the 
other  hand,  some  plants 
thrive  in  the  shade.  Such 
plants  are  the  mosses  and 
ferns.  Still  other  plants, 
minute  organisms  hardly 
visible  to  the  eye,  do  not 
thrive  in  the  Hght,  and 
may  be  killed  by  its  influence.  Such  are  molds,  mildews,  and 
some   bacteria.      Such   plants,    however,    are   not  green.      As  a 


The  growth  of  young  stems  and  leaves  of  oxalis 
toward  the  light. 


Two  stages  in  an  experiment  to  show  that  green  plants  grow  toward  the  light. 


matter  of  fact,  the  stem  of  a  green  plant  which  has  but  little 
chlorophyll  develops  somewhat  more  rapidly  under  conditions 
where  it  receives  no  light. 


LEAVES  AND   THEIR  WORK 


117 


Heliotropism.  —  We  saw  that  the  stems  of  the  plants  kept  in 
the  darkness  did  not  always  lift  themselves  erect,  as  in  the  case  of 
stems  in  the  light.  If  seedlings  have  been  growing  on  a  window 
sill,  or  where  the  light  comes  in  from  one  side,  you  have  doubtless 
noticed  that  the  stem  and  leaves  of  the  seedlings  incline  in  the 
direction  from  which  the  hght  comes.  The  tendency  of  young  stems 
and  leaves  to  grow  toward  sunlight  is  called  positive  heliotropism. 

The  experiment  pictured  on  the  preceding  page  shows  this  effect 
of  light  very  plainly.  A  hole  was  cut  in  one  end  of  a  cigar  box 
and  barriers  were  erected  in  the  interior  of  the  box  so  that  the  seeds 
planted  in  the  sawdust  received  their  light  by  an  indirect  course. 
The  young  seedling  in  this  case  responded  to  the  influence  of  the 
stimulus  of  light  so  as  to  grow  out  finally  through  the  hole  in  the 
box  into  the  open  air.  This  growth  of  the  stem  to  the  light  is  of 
very  great  importance 
to  a  growing  plant, 
because,  as  we  shall 
see  later,  food-making 
depends  largely  on  the 
amount  of  sunlight  the 
leaves  receive. 

Effect  of  Light.  — 
We  have  already  found 
that  seedlings  grown 
in  total  darkness  are 
almost  yellow-white  in 
color,  that  the  leaves 
are  but  slightly  de- 
veloped, and  that  the 
stem  has  developed  far 
more  than  the  leaves. 
We  have  also  seen  that 
a  green  plant  will  grow 
toward  the  source  of 
light,  even  against 
great  odds.  It  is  a  matter  of  common  knowledge  that  green 
leaves  turn  toward  the  light.  Place  growing  pea  seedlings,  oxalis, 
or  any  other  plants  of  rapid  growth  near  a  window  which  receives 


-  '■     i,                           -'^ 

I.*^'  'V  ^ 

Tall  straight  stems  of  the  hemlock  ;   the  trees  reach 
up  toward  the  source  of  light. 


118 


LEAVES  AND   THEIR  WORK 


full  sunlight.     Within  a  short  time  the  leaves  are  found  to  be  in 
positions  to  receive  the  most  sunUght  possible. 

Arrangement  of  Leaves.  —  A  study  of  trees  in  any  park,  or  in 
the  woods,  shows  that  the  stems  of  trees  in  thick  forests  are  usually 
tall  and  straight  and  that  the  leaves  come  out  in  clusters  near  the 
top  of  the  tree.  The  leaves  lower  down  are  often  smaller  and  less 
numerous  than  those  near  the  top  of  the  tree.  Careful  observa- 
tion of  any  plant  growing  outdoors  shows  us  that  in  almost  every 
case  the  leaves  are  so  disposed  as  to  get  much  sunlight.     The  ivy 


A  lily,  showing  long,  narrow 
leaves. 


The  dandelion,  showing  a  whorled   arrange- 
ment of  long,  irregular  leaves. 


climbing  up  the  wall,  the  morning-glory,  the  dandelion,  and  the 
burdock  all  show  different  arrangements  of  leaves,  each  presenting 
a  large  surface  to  the  light.  Leaves  are  usually  definitely  arranged, 
fitting  in  between  one  another  so  as  to  present  their  upper  surface 
to  the  sun.  Such  an  arrangement  is  known  as  a  leaf  rnosaic.  Good 
examples  of  such  mosaics,  or  leaf  patterns,  are  seen  in  trees  having 
leaves  which  come  up  alternately,  first  on  one  side  of  a  branch,  then 
on  the  other.  Here  the  leaves  turn,  by  the  twisting  of  their  stalks, 
so  that  all  the  leaves  present  their  upper  surface  to  the  sun.  In 
the  case  of  the  dandelion,  a  rosette  or  whorled  cluster  of  leaves 
is  found.  In  the  horse-chestnut,  where  the  leaves  come  out  oppo- 
site each  other,  the  older  leaves  have  longer  petioles  than  the 


LEAVES   AND   THEIR  WORK 


119 


young  ones.  In  the  mullein  the  entire  plant  forms  a  cone.  The 
old  leaves  near  the  bottom  have  long  stalks,  and  the  little  ones 
near  the  apex  come  out  close  to  the  main  stalk.  In  every  case 
each  leaf  receives  a  large  amount  of  Ught.  Other  modifications 
of  these  forms  may  easily  be  found  on  any  field  trip. 

The  Sun  a  Source  of  Energy.  —  We  all  know  the  sun  is  a  source 
of  most  of  the  energy  that  is  released  on  this  earth  in  the  form  of 
heat  or  light.  Solar  engines  have  not  come  into  any  great  use  as 
yet,  because  fuel  is  cheaper.  Actual  experiments  have  shown  that 
vast  amounts  of  energy  are  given  to  the  earth.  When  the  sun 
is  in  the  zenith,  energy  equivalent  to  one  hundred  horse  power 
is  received  by  a  plot  Of  land  twenty-five  by  one  hundred  feet,  the 
size  of  a  city  lot.  Plants  receive  and  use  much  of  this  energy  by 
means  of  their  leaves. 

The  Structure  of  a  Leaf.  —  Let  us 
now  examine  with  some  detail  the 
structure  of  a  simple  leaf  of  a  dico- 
tyledonous plant. 

A    green    loaf    shows  usually    (1)    a 


Palmately-veined  leaf  of  the  maple. 


Tho  .skeleton  of  a  notted- 
veined  leaf  :  M.R.,  midrib ; 
P.,  the  leafstalk  or  petiole ; 
v.,  the  veins. 


flat,  broad  blade  which  may  take  almost  any  conceivable  shape ; 
(2)  a  stem  or  petiole  which  (3)  spreads  out  in  the  blade  in  a 


120 


LEAVES   AND   THEIR  WORK 


number  of  veins.     These  veins  usually  present  a  netted  appear- 
ance in  the  leaf  of  a  dicotyledon,  but  run  more  or  less  parallel 

to  one  another  in  the  blade  of 
a  monocotyledonous  leaf.  At 
the  base  of  the  leaf  may  be 
found  a  pair  of  outgrowths 
from  the  petiole  called  stipules. 
By  means  of  these  stipules  in 
the  rose  leaf,  for  example,  we 
are  able  to  know  that  the  leaf 
is  compound,  that  is,  each  of 
the  little  leaflike  parts  is  in 
reality   part   of   a   leaf   blade 


Palmately-conipound  leaf  of  rose,  show 
ing  stipules  (st). 


that  is  so  deeply  indented  that 
the  blade  is  cut  away  to  the 
midrib,  or  central  vein,  of  the  leaf  —  for  a  pair  of  stipules  is 
found  at  the  base  of  every  complete  leaf.  These  fall  off 
early  in  many  leaves. 

The  Cell  Structure  of  a  Leaf. 
—  The  under  surface  of  a  leaf 
seen     under     the     microscope 


Surface  view  of  epidermis  of  lower  sur- 
face of  a  leaf  ;  e,  ordinary  epidermal 
cell ;  fir,  guard  cell.  —  Tschirch. 


Section  of  a  leaf  ;  e,  epidermis ;  c,  cells 
containing  chlorophyll  bodies ;  p,  in- 
tercellular passages ;  g,  g,  guard 
cells  of  stoma. 


usually  shows  numbers  of  tiny  oval  openings.  These  are  called 
stomata  (singular  stoma).  Two  cells,  usually  kidney-shaped,  are 
found,  one  on  each  side  of  the  stoma.     These   are  the   guard 


LEAVES   AND   THEIR   WORK 


121 


cells.  By  change  in  shape  of  these  cells  the  opening  of  the 
stoma  is  made  larger  or  smaller.  Larger  irregular  cells  form 
the  epidermis,  or  outer  covering  of  the  leaf.  Study  of  the  leaf 
in  cross  section  shows  that  these  stomata  open  directly  into 
air  chambers  which  penetrate  between  and  around  the  loosely 
arranged  cells  composing  the  underpart  of  the  leaf.  The  upper 
surface  of  leaves  sometimes  contains  stomata,  but  more  often  they 
are  lacking.  The  under  surface  of  an  oak  leaf  of  ordinary  size 
contains  about  2,000,000.  Under  the  upper  epidermis  is  a  layer 
of  green  cells  closely  packed  together  (called  collectively  the  pali- 
sade  layer).  These  cells  are  more  or  less  columnar  in  shape.  Under 
these  are  several  rows  of  rather  loosely  placed  cells  just  mentioned. 
These  are  called  collectively  the  spongy  parenchyma.  If  we  hap- 
pen to  have  a  section  cut  through  a  vein,  we  find  this  composed 
of  a  number  of  tubes  made  up  of,  and  strengthened  by,  thick-walled 
cells.  The  veins  are  evidently 
a  continuation  of  the  tubes  of 
the  stem  out  into  the  blade 
or  the  leaf. 

Starch  made  by  a  Green 
Leaf.  —  If  we  examine  the 
palisade  layer  of  the  leaf,  we 
find  cells  which  are  almost 
cylindrical  in  form.  In  the 
protoplasm  of  such  cells  are 
found  a  number  of  little  green 
colored  bodies,  which  are  known 
as  chloroplasts  or  chlorophyll 
bodies.  If  we  place  the  leaf  in 
wood  alcohol,  wc  find  that  the 
bodies  still  remain,  but  that 
the  color  is  extracted,  going 
into  the  alcohol  and  giving  to 
it  a  beautiful  green  color.  The  chloroplasts  are,  indeed,  simply 
part  of  the  protoplasm  of  the  cell  colored  green.  If  the  plant 
is  kept  in  the  sun,  the  chloroplasts  keep  their  green  color,  but  in 
the  dark  this  color  is  gradually  lost.  These  bodies  are  of  the 
greatest  importance  directly  to  plants  and  indirectly  to  animals. 


A  h\(irangc;i  plant,  upf)!!  tho  k-aves  of 
which  disks  of  cork  have  been  pinned  in 
order  to  exclude  sunlight  from  the  leaf. 


122 


LEAVES  AND   THEIR   WORK 


The  chloroplasts,  by  means  of  the  energy  received  from  the  sun,  manu- 
facture starch  out  of  certain  raw  materials.  These  raw  materials  are 
soil  water,  which  is  passed  up  through  the  bundles  of  tubes  into  the 
veins  of  the  leaf  from  the  roots,  and  carbon  dioxide,  which  is  taken 
in  through  the  stomata  or  pores,  which  dot  the  under  surface  of 
the  leaf. 

Light  and  Air  necessary  for  Starch- Making.  —  If  we  pin  strips 
of  black  cloth,  such  as  alpaca,  over  some  of  the  leaves  of  a  growing 
geranium,  place  the  plant  in  a  sunny  window  for  two  or  three  days, 
and  then  remove  some  of  the  covered  leaves  after  a  day  of  bright 

sunlight,  we  find  after  ex- 
tracting the  chlorophyll 
with  wood  alcohol  (because 
the  chlorophyll  covers  up 
the  contents  of  the  cells) 
that  starch  is  present  only 
in  the  portions  of  the 
leaves  exposed  to  sunlight. 
From  this  experiment  we 
infer  that  the  sun  has 
something  to  do  with  starch- 
making  in  a  leaf.  The  ne- 
cessity of  air  for  starch- 
making  may  also  easily  be 
proved,  for  the  parts  of  leaves  covered  with  vaseline  will  be 
found  to  contain  no  starch,  while  parts  of  the  leaf  unvaselined 
but  exposed  to  the  sun  and  air  contain  starch. 

Air  is  necessary  for  the  process  of  starch-making  in  a  leaf, 
not  only  because  carbon  dioxide  gas  is  absorbed  (there  are  from 
three  to  four  parts  in  ten  thousand  present  in  the  atmosphere), 
but  also  because  the  protoplasm  of  the  leaf  is  alive  and  must  have 
oxygen.     This  it  takes  from  the  air  around  it. 

Comparison  of  Starch-Making  and  Milling.  —  The  manufacture 
of  starch  by  the  green  leaf  is  not  easily  understood.  The  process 
has  been  compared  to  the  milling  of  grain.  In  this  case  the  mill  is 
the  green  part  of  the  leaf.  The  sun  furnishes  the  motive  power,  the 
chloroplasts  constitute  the  machinery,  and  soil  water  and  carbon 
dioxide  are  the  raw  products  taken  into  the  mill.    The  manufactured 


Starchless  areas  in  leaves  caused  by  excluding 
sunlight  by  means  of  strips  of  black  cloth. 


LEAVES   AND   THEIR   WORK 


m 


product  is  starch,  and  a  certain  by-product  (corresponding  to  the 
waste  in  a  mill)  is  also  given  out.  This  by-product  is  oxygen.  To 
understand  the  process 
fully,  we  must  refer  to  a 
small  portion  of  the  leaf. 
Here  we  find  that  the  cells 
of  the  green  layer  of  the 
leaf,  under  the  upper  epi- 
dermis, perform  most  cf 
the  work.  The  carbon 
dioxide  is  taken  in  through 
the  stomata  and  reaches 
the  green  cells  by  way 
of  the  intercellular  spaces 
and  by  diffusion  from  cell 
to  cell.  Water  reaches 
the  green  cells  through  the 
tracheal  tubes  of  the  veins. 
It  then  passes  into  the  cells        ^^8™°»  ^  ^"^^'^^^  *^«  formation  of  starch. 

by  osmosis,  and  there  becomes  part  of  the  cell  sap.     The  light 
of  the  sun  easily  penetrates  to  the  cells  of  the  palisade  layer, 


Diagram   (after  Stevens)   to  illustrate  the  processes  of  breathing,   food-maJcing, 
and  transpiration  which  may  take  place  in  the  cells  of  a  green  leaf  in  the  sunlight. 


124 


LEAVES  AND   THEIR  WORK 


giving  the  energy  needed  to  make  the  food.  This  whole  process 
is  a  very  delicate  one,  and  will  take  place  only  when  external  con- 
ditions are  favorable.  For  example,  too  much  heat  or  too  little 
heat  stops  starch-making ;  the  presence  of  stored  food  in  the  leaf, 
or  of  too  much  carbon  dioxide  in  the  atmosphere,  may  stop  its 
work.  This  building  up  of  food  and  the  release  of  oxygen  by 
the  plant  in  the  presence  of  sunlight  is  called  photosynthesis. 

Chemical  Action  in  Starch-Making.  —  In  the  process  of  starch-making 
in  a  leaf,  water  (H2O)  and  carbon  dioxide  (CO2)  are  combined  in  such  a 
way  as  to  make  starch,  the  molecule  of  which  is  expressed  by  the  formula 
CeHioOs.  This  combination  is  expressed  as  follows :  5  H2O  +  6  CO2  = 
CeHioOg  +  12  O.  The  starch  thus  formed  is  either  stored  in  the  leaf  or 
changed  by  digestion  to  some  form  which  can  pass  by  osmosis  from  cell  to 

cell ;  that  is,  a  soluble  material 
like  grape  sugar.  The  oxygen 
is  passed  off  through  the  stomata 
of  the  leaf.i 

Proteid-Making  and  its  Re- 
lation to  the  Making  of  Living 
Matter.  —  Proteid  material  is 
a  food  which  is  necessary  to 
form  protoplasm.  Proteid 
food  is  present  in  the  leaf,  and 
is  found  in  the  stem  or  root  as 
well.  Proteids  can  apparently 
be  manufactured  in  any  plant 
cells,  the  presence  of  light  not 
seeming  to  be  a  necessary 
factor.  How  it  is  manufac- 
tured is  a  matter  of  conjecture. 
The  minerals  brought  up  in 
the  soil  water  form  part  of 
its  composition,  and  starch  or 
grape  sugar  give  three  elements.  The  element  nitrogen  is  taken 
up  by  the  roots  as  a  nitrate  (nitrogen  in  combination  with  lime  or 


An  oxaniple  of  how  a  tree  may  exert 
energy.  This  rock  has  been  spHt  by  the 
growing  tree. 


^  It  seems  probable  that  food  material  is  first  made  in  the  form  of  a  sugar,  then 
changed  to  starch ;  when  transported  from  one  part  of  the  plant  to  another,  it  is 
changed  back  to  sugar. 


LEAVES  AND   THEIR   WORK 


125 


potash).  Proteids  are  probably  not  made  directly  into  proto- 
plasm in  the  leaf,  but  are  stored  by  the  cells  of  the  plant  and  used 
when  needed,  either  to  form  new  cells  in  growth  or  to  repair  waste. 
While  plants  and  animals  obtain  their  food  in  different  waj^s, 
they  probably  make  it  into  living  substance  (assimilate  it)  in 
exactly  the  same  manner. 

Foods  serve  exactly  the  same  purposes  in  plants  and  in  animals ; 
they  either  build  living  matter  or  they  are  burned  (oxidized)  to 
furnish  energy  (work  power).  If  you  doubt  that  a  plant  exerts 
energy,  note  how  the  roots  of  a  tree  bore  their  way  through  the  hard- 
est soil,  and  how  stems  or  roots  of  trees  often  split  open  the  hardest 
rocks,  as  illustrated  on  the  opposite  page. 

Rapidity  of  Starch- Making.  —  Leaves  which  have  been  in  dark- 
ness soon  show  starch  to  be  present  when  exposed  to  light.  Squash 
leaves  make  three  fourths  of  an  ounce  for  each  square  yard  of  sur- 
face. A  corn  plant  sends  10  to  15 
grams  of  reserve  material  into  the 
ears  in  a  single  day.  The  formation 
of  fruit,  and  especially  the  growth  of 
the  grain  fields,  show  the  economic 
importance  of  this  fact.  Not  only  do 
plants  make  their  own  food  and  store 
it  away,  but  they  make  food  for 
animals  as  well.  And  the  food  is 
stored  in  such  a  stable  form  that  it 
may  be  sent  to  all  parts  of  the  world 
in  the  form  of  grain  or  other  fruits. 
Animals,  herbivorous  and  flesh- 
eating,  man  himself,  all  are  depend- 
ent upon  the  starch-making  processes 
of  the  green  plant  for  the  ultimate 
source  of  their  food. 

Oxygen  given  off  by  Green  Plants.  — 
It  is  possible  to  prove  that  oxygen  is 
given  off  by  green  plants  in  sunlight. 
The  common  green  frog  scum  seen  in 

,     ,,  ,     .        -,  /•   11     /•  1     1  i_i  Experiment  to  show  that  oxygen 

shallow  ponds  is  often  so  full  of  bubbles  -^  ^^^^  ^^  ^y  green  plants  in 

that  it  is  buoyed  up  by  this  means  at       the  sunHght.    o,  oxygen. 


126 


LEAVES  AND   THEIR   WORK 


the  water's  surface.  If  some  of  this  plant  or  other  green  water 
weed  is  placed  in  a  large  battery  jar  or  fruit  jar  in  a  sunny- 
window,  bubbles  of  gas  will  be  seen  to  arise  from  it,  the  amount 
increasing  as  the  water  is  warmed  by  the  sun's  rays. 

If  a  glass  funnel  is  placed  upside  down  so  as  to  cover  the  plants, 
and  then  a  test  tube  full  of  water  inverted  over  the  mouth  of  the 
funnel,  the  gas  may  be  collected  by  displacement.  After  two  or 
three  days  of  hot  sun,  enough  of  the  gas  can  be  obtained  to  make 
the  oxygen  test. 

That  oxygen  is  given  off  as  a  by-product  by  green  plants  is  a  fact 
of  far-reaching  importance.  Parks  are  in  a  city  true  "  breathing 
spaces."  The  green  covering  of  the  earth  is  giving  to  animals  an 
element  that  they  must  have,  while  the  animals  in  their  turn  are 

supplying  to  the  plants  carbon 
dioxide,  a  compound  used  in 
food-making.  Thus  a  relation 
of  mutual  helpfulness  exists 
between  plants  and  animals. 

Evaporation  of  ExcessWater. 
—  In  the  manufacture  of  starch 
and  proteid,  an  enormous 
amount  of  water  is  taken  up 
by  the  roots  and  passed  to 
the  leaves  to  supply  the 
needed  amount  of  mineral 
matter.  The  excess  of  water 
is  evaporated  through  the  sto- 
mata.  That  water  is  passed 
through  the  blade  of  the  leaf 
in  the  form  of  moisture  is 
shown  by  the  photograph 
above,  drops  of  water  having 
gathered  on  the  inside  of  the 
bell  jar.  A  small  grass  plant 
on  a  summer's  day  evaporates 
more  than  its  own  weight  in 
water.  This  would  make 
nearly  half    a    ton  of  water 


Experiment  to  show  transpiration.  Notice 
that  roots  covered  with  root  hairs  have 
grown  out  of  the  main  stem  of  the  plant 
in  response  to  the  moist  condition  exist- 
ing outside  of  the  rubber-covered  flower- 
pot and  within  the  bell  jar. 


LEAVES  AND   THEIR   WORK 


127 


distributed  to  the  air  during  twenty-four  hours  by  a  grass  plot 
twenty-five  by  one  hundred  feet,  the  size  of  the  average  city  lot. 
According  to  Ward,  an  oak  tree  may  pass  off  two  hundred  and 
twenty-six  times  its  own  weight  in  water  during  the  season  from 
June  to  October. 

From  which  Surface  of  the  Leaf  is  Water  Lost?  —  In  order  to  find  out 
whether  water  is  passed  out  from  any  particular  part  of  the  leaf,  we  may  re- 
move two  leaves  of  the  same  size  and  weight  from  some  large-leaved 
plant  —  a  mullein  was  used  for  the  illustrations  given  below  —  and  cover  the 


1  xperiiiient  to  show  through  which  surface  of  a  leaf  water  passes  off. 

• 

upper  surface  of  one  leaf  and  the  lower  surface  of  the  other  with  vaseline. 
The  petioles  of  each  should  be  covered  with  wax  or  vaseline,  and  the 
two  leaves  exactly  balanced  on  the  pans  of  a  balance  which  has  previously 
been  placed  in  a  warm  and  sunny  place.  Within  an  hour  the  leaf  which 
has  the  upper  surface  covered  with  vaseline  will  show  a  loss  of  weight. 
Examination  of  the  surface  of  a  mullein  leaf  shows  us  that  the  lower  sur- 
face of  the  leaf  is  provided  with  stomata.  It  is  through  these  organs, 
then,  that  water  is  passed  out  from  the  tissues  of  the  leaf. 

Regulation  of  Transpiration.  —  The  stomata  of  leaves  close  at  night. 
On  days  when  there  is  little  humidity,  they  also  tend  to  close,  retarding 
transpiration,  but  when  the  water  supply  is  abundant  they  open,  increas- 
ing transpiration.  This  automatic  action  is  of  very  great  importance  to 
the  life  of  a  plant,  since  evaporation  of  water  is  thus  regulated. 

The  Effect  of  Transpiration  on  Water  within  the  Stem.  —  It  has  al- 
ready been  noted  that  root  pressure  alone  will  not  account  for  the  rise 


128 


LEAVES  AND   THEIR   WORK 


of  water  to  the  tops  of  very  tall  trees.  Experiments  show  that  evapora- 
tion of  water  through  the  stomata  exerts  a  lifting  power  upon  the  fluids 
within  the  stem  of  the  tree,  thus  aiding  in  the  raising  of  water  to  the  leaves 
in  the  upper  branches. 


a  b  c 

Diagrams  of  a  stoma  :  a,  surface  view  of  an  opened  stoma ;  b,  same  stoma  closed 
(after  Hansen)  ;  c,  diagram  of  a  transverse  section  through  a  stoma  —  dotted 
lines  indicate  the  closed  position  of  the  guard  cells,  the  heavy  lines  the  open 
condition.     (After  Schwendener.) 

Respiration  by  Leaves.  —  All  li\ang  things  require  oxygen.  It 
is  by  means  of  the  oxidation  of  food  materials  within  the  plant's 
body  that  the  energy  used  in  growth  and  movement  is  released.  A 
plant  takes  in  oxygen  largely  through  the  stomata  of  the  leaves, 
to  a  less  extent  through  the  lenticels  in  the  stem,  and  through 
the  roots.  Thus  rapidly  growing  tissues  receive  the  oxygen  neces- 
sary for  them  to  perform  their  work.  The  products  of  oxidation 
in  the  form  of  carbon  dioxide  are  also  passed  off  through  these 
same  organs.  It  can  be  shown  by  experiment  that  a  plant  uses  up 
oxygen  in  the  darkness ;  in  the  light  the  amount  of  oxygen  given 
off  as  a  by-product  in  the  process  of  starch-making  is,  of  course, 
much  greater  than  the  amount  used  by  the  plant. 

Summary.  —  From  the  above  paragraphs  it  is  seen  that  a  leaf 
performs  the  following  functions :  (1)  breathing,  or  the  taking  in 
of  oxygen  and  passing  off  of  carbon  dioxide;  (2)  starch-making, 
with  the  incidental  passing  out  of  oxygen ;  (3)  formation  of  proteids, 
with  their  digestion  and  assimilation  to  form  new  tissues;  and  (4)  the 
transpiration  of  water. 

Economic  Uses  of  Leaves. — The  practical  use  of  green  plants  to 
man  is  very  great.  Plants  give  off  oxygen  in  the  sunlight  and  use 
carbon  dioxide,  which  is  given  off  by  animals  in  the  breath.  We 
should  remember,  as  taxpayers,  that  money  invested  in  public  parks 
is  money  well  invested,  bringing  as  it  does  a  source  of  oxygen  supply 
where  it  is  most  needed,  in  the  congested  parts  of  our  great  cities. 


LEAVES   AND   THEIR   WORK 


129 


Another  very  important  use  to  man  is  seen  in  the  fact  that  leaves, 
falhng  to  the  ground,  help  to  form  a  rich  covering  of  humus,  which 
acts  as  a  coat  to  hold  in  moisture.  The  forests  are  our  greatest 
source  of  water  supply.  The  cutting  away  of  the  forest  always 
means  a  depletion  of  the  reserve  water  stored  in  soil,  with  conse- 
quent floods  and  droughts  in  alternation. 

Leaves  are  used  directly  by  man  for  food.  Examples  are  cab- 
bage, lettuce,  kale,  broccoli,  and  some  others.  These  foods, 
properly  admixed  with  certain  fleshy  foods,  are  of  great  importance 
in  giving  a  balance  to  diet.  In  a  wider  sense,  all  animals  depend 
upon  leaves  for  their  food  supply 
either  directly,  —  for  herbivorous  ani- 
mals feed  upon  the  leaves  of  plants 
— or  indirectly  in  foods  obtained  from 
roots,  stems,  seeds,  and  fruits.  For 
in  every  case  the  stored  food  has  been 
manufactured  in  the  leafy  part  of  the 
plant  and  transported  within  the  plant 
to  its  place  of  storage.  Even  meat- 
eating  animals  are  in  the  long  run 
dependent  upon  plants,  for  they  feed 
upon  plant  eaters. 

Modified  Leaves.  —  In  many  plants  the 
leaves  are  reduced  to  spines  or  have  part 
of  the  leaf  modified  so  as  to  form  spines. 
In  some  leaves  this  appears  to  be  for  pro- 
tection against  animals,  but  in  some  cases, 
as  the  cactus,  it  is  a  means  of  protecting 
the  plant  against  loss  of  water  through 
evaporation. 

If  a  cactus  is  cut  open,  it  will  be  found 
to  contain  a  very  considerable  amount  of 
water.  The  Indians  of  the  New  Mexican 
desert  region,  when  far  from  a  source  of 
water,  sometimes  cut  oflf  the  top  of  a  large 

cactus,  mash  up  the  soft  interior  of  the  thickened  stem,  squeeze  out  the 
pulp,  and  thus  obtain  several  quarts  of  drinkable  water. 

Protection  by  Hairs.  —  In  the  muUein,  one  of  our  hardiest  weeds,  the 
leaf  is  covered  with  a  coating  of  finely  branched  hairs.  Might  such  a 
covering  be  of  use  to  the  leaf?     In  what  ways? 

HUNT.   E8.    BIO. 9 


A   cactus,    showing   the   leaves 
modified  into  spines. 


130 


LEAVES   AND   THEIR   WORK 


Storage  of  Food  and  Water  in  Leaves.  —  Leaves  may  be  modified  for 
the  storage  of  food  and  water.  Test  an  onion,  which  is  a  collection  of 
thickened  leaves  closely  wrapped  to  form  what  is  called  a  bulb,  for  starch, 

sugar,  and  proteid.  Squeeze  any 
fleshy  leaves  and  notice  the  water 
contained  in  them.  The  agave  is  a 
desert  plant  in  which  the  leaves  have 
become  greatly  thickened  as  a  water 
and  food  storage. 

Leaves  modified  for  Use  in  Climb- 
ing. —  Sometimes,  as  in  the  leaf  of 
the  pea,  a  part  of  the  leaf  is  modified 
for  the  purpose  of  climbing.  In  this 
case  a  part  of  the  leaf,  called  the 
tendril,  becomes  especially  sensitive 
to  the  stimulus  of  touch,  and  upon 
touching  an  object  slowly  coils  around 
it.  Almost  any  part  of  the  leaf,  or 
indeed  the  entire  leaf,  may  be  modi- 
fied to  become  a  tendril. 

Reduced  Leaves.  —  Leaves  may 
be  reduced  to  scales  or  lost  al- 
together. In  the  asparagus,  what 
seem  to  be  tiny  leaves  are  branches 
which  spring  from  the  axils  of  the 
true,  very  tiny,  scalelike  leaves. 

Leaves  as 
Insect  Traps. 
— Most  curious 
of  all  are  the  modifications  of  the  leaf  into  insect 
traps.  It  frequently  happens  that  the  habitat  of  a 
plant  will  not  furnish  the  raw  food  materials  ne- 
cessary to  form  proteid  food  and  to  build  proto- 
plasm. Nitrogen  is  the  lacking  element.  The 
plant  has  become  adapted  to  these  conditions  and 
obtains  nitrogenous  food  from  the  bodies  of  insects 
which  it  catches.  Examples  of  insect  traps  are 
the  common  bladderwort  (utricularia),  the  Venus's 
flytrap  {Dioncea  muscipula) ,  the  sundew  (Drosera 
rotundifolia) ,  and  certain  of  the  pitcher  plants. 

Bladderwort.  —  The  simplest  contrivance  for  the    ^^^^  captured  insect. 
taking  of  animal  food   by  the  leaf  is  seen  in  the 

bladderwort.  Here  certain  of  the  leaves  are  modified  into  little  bladders 
provided  with  trapdoors  which  open  inwards.  Small  water-swimming 
crustaceans  (as  water  fleas,  etc.)  push  their  way  into  the  trap  and  there 


Bladderwort,  showing  finely  dissected 
submerged  leaves  bearing  blades 
which  capture  little  animals. 


Leaf  of  sundew  closing 


LEAVES  AND   THEIR   WORK 


lai 


die,  perhaps  of  starvation.  Bacteria,  causing  decay,  soon  break  down 
their  bodies  into  soluble  substances,  the  nitrogenous  portion  of  which 
is  absorbed  by  the  inner  surface  of  the  bladders  and  used  by  the 
plant  as  food. 

Venus's  Flytrap.  —  In  the  Venus's  flytrap,  a  curious  plant  found  in 
our  Southern  states,  the  apex  of  the  leaf  is  peculiarly  modified  to  form  an 
insect  trap.  Each  margin  of 
the  leaf  is  provided  with  a 
row  of  hairs ;  there  are  also 
three  central  hairs  on  each 
side  of  the  midrib.  The 
hairs  are  sensitive  to  a 
stimulus  from  without.  The 
blade  is  so  constructed  that 
the  slightest  stimulus  causes 
a  closing  of  the  leaf  along 
the  midrib.  The  surface  of 
the  leaf  is  provided  with 
many  tiny  glands,  which  pour 
out  a  fluid  capable  of  digest- 
ing proteid  food.  Thus  an 
insect,  caught  between  the 
halves  of  the  leaf  blade,  is 
held  there  and  slowly  digested. 

Sundew.  —  In  the  sundew 
the  leaves  are  covered  with 
long  glandular  hairs,  each  of 
which  is  extremely  sensitive 
to  the  stimulus  of  any  nitrog- 
enous substance.  These 
hairs  exude  a  clear,  sticky 
fluid  which  first  renders 
more  difficult  the  escape  of 
the  insect  caught  in  the  hairs, 
and  then  digests  the  nitrog- 
enous parts  of  the  insect 
thus  caught. 

Pitcher  Plants.  —  The  common  pitcher  plant  has  an  urn-shaped  leaf 
which  is  modified  to  hold  water.  Many  small  flies  and  other  insects 
find  their  way  into  the  pitcher  and  are  eventually  drowned  in  the  cup. 
Whether  the  plant  actually  makes  use  of  the  food  thus  obtained  is  a 
matter  unsettled,  but  some  tropical  forms  undoubtedly  do  use  the  caught 
insects  as  food. 


Pitcher  plant :  a,  leaf ;  b,  cross  section ;  c,  longi- 
tudinal section.  Note  the  insects  at  the  bottom, 
and  the  inward-pointing  hairs  at  the  top. 


132  LEAVES  AND   THEIR  WORK 


Reference  Books 

elementary 

Sharpe,  A  Laboratory  Manual  for  the  Solution  of  Problems  in  Biology,    American 

Book  Company. 
Andrews,  Botany  all  the  Year  Round,  pages  46-62.     American  Book  Company. 
Coulter,  A  Textbook  of  Botany,  pages  5-40.     D.  Appleton  and  Company. 
Dana,  Plants  and  their  Children,  pages  135-185.     American  Book  Company. 
Stevens,  Introduction  to  Botany,  pages  81-99.     D.  C.  Heath  and  Company. 

ADVANCED 

Clement,  Plant  Physiology  and  Ecology.     Henry  Holt  and  Company. 

Coulter,  Barnes,  and  Cowles,  A  Textbook  of  Botany,  Part  II,  and  Vol.  II.  American 
Book  Company. 

Darwin,  Insectivorous  Plants.     D.  Appleton  and  Company. 

Goodale,  Physiological  Botany,  pages  337—353  and  409—424.  American  Book  Com- 
pany. 

Green,  Vegetable  Physiology.     J.  and  A.  Churchill. 

Lubbock,  Flowers,  Fruits,  and  Leaves,  last  part.     The  Macmillan  Company. 

MacDougal,  Practical  Textbook  of  Plant  Physiology.  Longmans,  Green,  and  Com- 
pany. 

Report  of  the  Division  of  Forestry,  U.S.  Department  of  Agriculture,  1899. 

Strasburger,  Noll,  Schenck,  and  Schimper.  A  Textbook  of  Botany.  The  Mac- 
millan Company. 

Ward,  The  Oak.    D.  Appleton  and  Company. 


X.   OUR  FORESTS;  THEIR  USES   AND  THE  NECESSITY 
FOR  THEIR   PROTECTION 

Problem  XIX.    Some  uses  of  stems  {optional).    {Ldbordtory 
Manual,  Prob.  XIX.) 
{a)    Special  product  from  stems. 

(b)  Some  woods  and  their  value. 

(c)  Field  work  in  forestry. 

The  Economic  Value  of  Trees.  Protection  and  Regulation  of 
Water  Supply.  —  Trees  form  a  protective  covering  for  the  earth's 
surface.  They  prevent  soil  from  being  washed  away,  and  they  hold 
moisture  in  the  ground.  Without  trees  many  of  our  rivers  might 
go  dry  in  summer,  while  in  the  rainy  season  sudden  floods  would 
result.  The  devastation  of 
immense  areas  in  China  and 
considerable  damage  by 
floods  in  parts  of  Switzer- 
land, France,  and  in  Penn- 
sylvania has  resulted  where 
the  forest  covering  has  been 
removed.  No  one  who  has 
tramped  through  our  Adi- 
rondack forest  can  escape 
noticing  the  differences  in 
the  condition  of  streams 
which  flow  through  areas 
covered  with  forest  and  those  from  around  which  trees  have 
been  cut.  The  latter  streams  often  dry  up  entirely  in  hot 
weather,  while  the  forest-shaded  stream  has  a  never  failing 
supply  of  crystal  water. 

The  city  of  New  York  owes  much  of  its  importance  to  its  posi- 
tion at  the  mouth  of  a  great  river  with  a  harbor  large  enough  to 
float  the  navies  of  the  world.     This  river  is  supplied  with  water 

133 


Working  to  prevent  erosion  after  the  removal 
of  the  forest  in  the  French  alps. 


134 


OUR   FORESTS 


largely  by  the  Adirondack  and  Catskill  forests.  Should  these 
forests  be  destroyed,  it  is  not  impossible  that  the  frequent  freshets 
which  would  follow  would  so  fill  the  Hudson  River  with  silt  and 

debris  that  the  ship 
channels  in  the  bay, 
already  costing  the 
government  millions  of 
dollars  a  year  to  keep 
dredged,  would  become 
too  shallow  for  ships. 
If  this  should  occur, 
the  greatest  city  in  this 
country  would  soon  lose 
its  place  and  become  of 
second-rate  importance. 
The  story  of  how  this 
very  thing  happened  to 
the  old  Greek  city  of  Poseidonia  is  graphically  told  in  the  following 
lines :  — 

*'  It  was  such  a  strange,  tremendous  story,  that  of  the  Greek  Posei- 
donia, later  the  Roman  Psestum.  Long  ago  those  adventuring  mariners 
from  Greece  had  seized  the  fertile  plain  which  at  that  time  was  covefed 
with  forests  of  great  oak  and  watered  by  two  clear  and  shining  rivers. 
They  drove  the  Italian  natives  back  into  the  distant  hills,  for  the  white 
man's  burden  even  then  included  the  taking  of  all  the  desirable  things 
that  were  being  wasted  by  incompetent  natives,  and  they  brought  over 
colonists  —  whom  the  philosophers  and  moralists  at  home  maligned,  no 
doubt,  in  the  same  pleasant  fashion  of  our  own  day.  And  the  colonists 
cut  down  the  oaks,  and  plowed  the  land,  and  built  cities,  and  made  harbors, 
and  finally  dusted  their  busy  hands  and  busy  souls  of  the  grime  of  labor 
and  wrought  splendid  temples  in  honor  of  the  benign  gods  who  had  given 
them  the  possessions  of  the  Italians  and  filled  them  with  power  and  fat- 


Eiosiou  at  Sayre,   Penn.,   by  the  Chemung  River. 
Photograph  by  W.  C.  Barbour. 


"  Every  once  in  so  often  the  natives  looked  lustfully  down  from  the 
hills  upon  this  fatness,  made  an  armed  snatch  at  it,  were  driven  back  with 
bloody  contumely,  and  the  heaping  of  riches  upon  riches  went  on.  And 
more  and  more  the  oaks  were  cut  down  —  mark  that !  for  the  stories  of 
nations  are  so  inextricably  bound  up  with  the  stories  of  trees  —  until  all 
the  plain  was  cleared  and  tilled  ;  and  then  the  foothills  were  denuded,  and 
the  wave  of  destruction  crept  up  the  mountain  sides,  and  they,  too,  were 
left  naked  to  the  sun  and  the  rains. 


OUR  FORESTS  135 

"  At  first  these  rains,  sweeping  down  torrentially,  unhindered  by  the 
lost  forests,  only  enriched  the  plain  with  the  long-hoarded  sweetness  of 
the  trees  ;  but  by  and  by  the  Uving  rivers  grew  heavy  and  thick,  vomiting 
mud  into  the  ever  shallowing  harbors,  and  the  land  soured  with  the  un- 
drained  stagnant  water.  Commerce  turned  more  and  more  to  deeper 
ports,  and  mosquitoes  began  to  breed  in  the  brackish  soil  that  was  making 
fast  between  the  city  and  the  sea. 

"  Who  of  all  those  powerful  landowners  and  rich  merchants  could  ever 
have  dreamed  that  little  buzzing  insects  could  sting  a  great  city  to  death  ? 
But  they  did.  Fevers  grew  more  and  more  prevalent.  The  malaria- 
haunted  population  went  more  and  more  languidly  about  their  business. 
The  natives,  hardy  and  vigorous  in  the  hills,  were  but  feebly  repulsed. 
Carthage  demanded  tribute,  and  Rome  took  it,  and  changed  the  city's 
name  from  Poseidonia  to  Paestum.  After  Rome  grew  weak,  Saracen 
corsairs  came  in  by  sea  and  grasped  the  slackly  defended  riches,  and  the 
little  winged  poisoners  of  the  night  struck  again  and  again,  until  grass 
grew  in  the  streets,  and  the  wharves  crumbled  where  they  stood.  Finally, 
the  wretched  remnant  of  a  great  people  wandered  away  into  the  more 
wholesome  hills,  the  marshes  rotted  in  the  heat  and  g^ew  up  in  coarse 
reeds  where  corn  and  vine  had  flourished,  and  the  city  melted  back  into 
the  wasted  earth." 

Elizabeth  Bisland  and  Anne  Hoyt,  Seekers  in  Sicily.    John  Lane  Company. 

Prevention  of  Erosion  by  Covering  of  Organic  Soil.  —  We  have 
shown  how  ungovernecl  streams  might  dig  out  soil  and  carry  it 
far  from  its  original  source.  Examples  of  what  streams  have  done 
may  be  seen  in  the  deltas  formed  at  the  mouths  of  great  rivers. 
The  forest  prevents  this  by  holding  the  water  supply  and  letting  it 
out  gradually.  This  it  does  by  covering  the  inorganic  soil  with 
humus  or  decayed  organic  material.  In  this  way  the  forest 
floor  becomes  like  a  sponge,  holding  water  through  long  periods 
of  drought.  The  roots  of  the  trees,  too,  help  hold  the  soil  in  place. 
The  gradual  evaporation  of  water  through  the  stomata  of  the  leaves 
cools  the  atmosphere,  and  this  tends  to  precipitate  the  moisture 
in  the  air.  Eventually  the  dead  bodies  of  the  trees  themselves  are 
added  to  the  organic  covering,  and  new  trees  take  their  place. 

Other  Uses  of  the  Forest.  —  In  some  localities  forests  are  used  as 
A\indbreaks  and  to  protect  mountain  towns  against  avalanches. 
In  winter  they  moderate  the  cold,  and  in  summer  reduce  the  heat 
and  lessen  the  danger  from  storms.  The  nesting  of  birds  in  woods 
protects  many  plants  valuable  to  man  which  other^vise  might  be 
destroyed  by  insects. 


136 


OUR   FORESTS 


Forests  have  great  commercial  importance  as  well.  Even  in  this 
day  of  coal,  wood  is  still  by  far  the  most-used  fuel.  It  is  useful  in 
building.  It  outlasts  iron  under  water,  in  addition  to  being  durable 
and  light.  It  is  cheap  and,  with  care  of  the  forests,  inexhaustible, 
while  our  mineral  wealth  will  some  day  be  used  up.  Hard  woods  are 
chiefly  used  in  house  building  and  furniture  manufacture ;  the  soft 
woods,  reduced  to  pulp,  are  made  into  paper.  Distilled  wood  gives 
alcohol.  Partially  burned  wood  is  charcoal.  Vinegar  and  other 
acids  are  obtained  from  trees,  as  are  tar,  creosote,  resin,  turpentine, 
and  other  useful  oils.  The  making  of  maple  sirup  and  sugar  forms  a 
profitable  industry  in  several  states. 


FOREST    REGIONS       \ 


The  forest  regions  of  the  United  States. 


The  Forest  Regions  of  the  United  States.  —  The  combined  area 
of  all  the  forests  in  the  United  States,  exclusive  of  Alaska,  is  about 
500,000,000  acres.  This  seemingly  immense  area  is  rapidly  de- 
creasing in  acreage  and  in  quality,  thanks  to  the  demands  of  an 
increasing  population,  a  woeful  ignorance  on  the  part  of  the  owners 
of  the  land,  and  wastefulness  on  the  part  of  cutters  and  users  alike. 

A  glance  at  the  map  shows  the  distribution  of  our  principal 
forests.  The  following  figures  taken  from  the  United  States  Census 
reports    tell    their    own    tale.      In    1908,   31,231    sawmills    cut 


OUR  FORESTS 


137 


33,289,369,000  feet  of  lumber.  They  also  cut  over  12  billion 
shingles  and  nearly  30  billion  laths.  Nobody  can  tell  how  much 
lumber  was  wasted,  either  in  the  forest  or  at  the  mill.  The  census 
estimates,  moreover,  that  owing  to  conditions  caused  by  the  panic, 
the  amount  cut  was  very  considerably  under  that  cut  in  1907. 
Washington  ranks  first  in  the  production  of  lumber.  Here  the 
great  Douglas  fir,  one  of  the  "  evergreens,"  forms  the  chief 
source  of  supply.  In  the  Southern  states,  especially  Louisiana 
and  Mississippi,  yellow  pine  and  cypress  are  the  trees  most 
lumbered. 

Uses  of  Wood.  —  In  our  forests  much  of  the  soft  wood  (the  cone- 
bearing  trees,  spruce,  balsam,  hemlock,  and  pine),  and  poplars, 
aspens,  basswood,  with 
some  other  species,  make 
paper  pulp.  The  daily 
newspaper  and  cheap  books 
are  responsible  for  inroads 
on  our  forests  which  cannot 
well  be  repaired.  It  is  not 
necessary  to  take  the  largest 
trees  to  make  pulp  wood. 
Hence  many  young  trees  of 
not  more  than  six  inches 
in  diameter  are  sacrificed. 
Of  the  hundreds  of  species  of  trees  in  our  forests,  the  conifers  are 
probably  most  sought  after  for  lumber.  Pine,  especially,  is  prob- 
ably used  more  extensively  than  any  other  wood.  It  is  used  in 
all  heavy  construction  work,  frames  of  houses,  bridges,  masts, 
spars  and  timber  of  ships,  floors,  railway  ties,  and  many  other 
purposes.  Cedar  is  used  for  shingles,  cabinetwork,  lead  pencils, 
etc. ;  hemlock  and  spruce  for  heavy  timbers  and,  as  we  have  seen, 
for  paper  pulp.  Another  use  for  our  lumber,  especially  odds  and 
ends  of  all  kinds,  is  in  the  packing-box  industry.  It  is  estimated 
that  nearly  50  per  cent  of  all  lumber  cut  ultimately  finds  its 
way  into  the  construction  of  boxes.  Hemlock  bark  is  used  for 
tanning. 

The  hard  woods,  ash,  basswood,  beech,  birch,  cherry,  chestnut, 
elm,  maple,  oak,  and  walnut,  are  used  largely  for  the  "  trim  "  of 


Transportation   of   lumber   in    the  West. 
logging  train. 


138 


OUR  FORESTS 


Transportation  of  lumber  in  the  East.      Logs  are  mostly  floated  down  rivers  to  the 

mills. 


our  houses,  for  manufacture  of  furniture,  wagon  or  car  work,  and 
endless  other  purposes. 

Structure  of  Wood.  —  Quite  a  difference  in  color  and  structure  is  often 
seen  between  the  heartwood,  composed  of  the  dead  walls  of  cells  occupy- 
ing the  central  part  of  the  tree  trunk,  and  the  sap  wood,  the  living  part 

of  the  stem.  In  trees  which  are  cut 
down  for  use  as  lumber  and  in  the 
manufacture  of  various  furniture,  the 
markings  and  differences  in  color  are 
not  always  easy  to  understand. 

Methods  of  cutting   Timber.  —  A 

glance  at  the  diagram  of  the  sections 

of  timber  show  us  that  a  tree  may  be 

cut   radially   through   the   middle   of 

the     trunk    or    tangentially    to     the 

„  5  c  middle  portion.     Most  lumber  is  cut 

Diagrams  of  sections  of  timber :  a,  cross     tangentially.     Hence  the  yearly  rings 

section;    6,    radial;    c,    tangential,      take  a  more  or  less  irregular  course. 

(From  Pinchot,  U.S.  Dept.  of  Agr.)      The  grain  of  wood  is  caused  by  the 


OUR  FORESTS 


139 


fibers  not  taking  straight  lines  in  their  course  in  the  tree  trunk.  In  many- 
cases  the  fibers  of  the  wood  take  a  spiral  course  up  the  trunk,  or  they 
may  wave  outward  to  form  little  projections.  Boards  cut  out  of  such  a 
piece  of  wood  will  show  the  effect  seen  in  many  of 
the  school  desks,  where  the  annual  rings  appear  to 
form  elUptical  markings. 

Knots.  —  Knots,  as  can  be  seen  from  the  diagram, 
are  branches  which  at  one  time  started  in  their 
outward  growth  and  were  for  some  reason  killed. 
Later,  the  tree,  continuing  in  its  outward  growth, 
surrounded  them  and  covered  them  up.  A  dead 
limb  should  be  pruned  before  such  growth  occurs. 
The  markings  in  bird's-eye  maple  are  caused  by 
adventitious  buds  which  have  not  developed,  and 
have  been  overgrown  with  the  wood  of  the  tree. 


Section  of  tree  trunk 
showing  knot. 


Destruction  of  the  Forest.  By  Waste  in  Cutting.  —  Man  is 
responsible  for  the  destruction  of  one  of  this  nation's  most  valuable 
assets.     This  is  primarily  due  to  wrong  and  wasteful  lumbering. 


A  forest  iu  the  far  West  totally  destroyed  by  fire  and  wasteful  lumberiug. 


Hundreds  of  thousands  of  dollars'  worth  of  lumber  is  left  to  rot  an- 
nually because  the  lumbermen  do  not  cut  the  trees  close  enough  to 
the  ground,  or  because  through  careless  felling  of  trees  many  other 


140 


OUR  FORESTS 


smaller  trees  are  injured.  There  is  great  waste  in  the  mills.  In  fact, 
man  wastes  in  every  step  from  the  forest  to  the  finished  product. 

By  Fire.  —  Indirectly,  man  is  responsible  for  fire,  one  of  the  great- 
est enemies  of  the  forest.  Most  of  the  great  forest  fires  of  recent 
years,  the  losses  from  which  total  in  the  hundreds  of  millions,  have 
been  due  either  to  railroads  or  to  carelessness  in  setting  fires  in  the 
woods.  It  is  estimated  that  in  forest  lands  traversed  by  railroads 
from  25  per  cent  to  90  per  cent  of  the  fires  are  caused  by  coal- 
burning  locomotives.  For  this  reason  laws  have  been  made  in 
New  York  state  requiring  locomotives  passing  through  the 
Adirondack  forest  preserve  to  burn  oil  instead  of  coal.  This 
has  resulted  in  a  considerable  reduction  in  the  number  of  fires.  In 
addition  to  the  loss  in  timber,  the  fires  often  burn  out  the  organic 
matter  in  the  soil  (the  ''duff  ")  forming  the  forest  floor,  thus  pre- 
venting the  growth  of  forest  there  for  many  years  to  come.  In  New 
York  and  other  states  fires  are  fought  by  an  organized  corps  of  fire 
wardens,  whose  duty  it  is  to  watch  the  forest  and  to  fight  forest  fires. 

Other  Enemies.  —  Other  enemies  of  the  forest  are  numerous 
fungous  plants  of  which  we  will  learn  more  later,  insect  parasites. 


Our  birds  help  protect  our  forests.     This  tree  has  been  attacked  by  boring  insects, 
but  woodpeckers  have  dug  them  out  and  killed  them. 


OUR  FORESTS  141 

which  bore  into  the  wood  or  destroy  the  leaves,  and  grazing  animals, 
particularly  sheep.     Wind  and  snow  also  annually  kill  many  trees. 

Forestry.  —  The  American  forests  have  long  been  our  pride. 
In  Germany,  especially,  the  importance  of  the  forest  has  long  been 
recognized,  and  the  German  forester  or  caretaker  of  the  forests  is 
well  known.  In  some  parts  of  central  Europe,  the  value  of  the 
forests  was  seen  as  early  as  the  year  1300  a.d.,  and  many  towns 
consequently  bought  up  the  surrounding  forests.  The  city  of 
Zurich  has  owned  forests  in  its  vicinity  for  at  least  600  years.  In 
this  country  only  recently  has  the  importance  of  preserving  and 
caring  for  our  forests  been  noted  by  our  government.  Now,  how- 
ever, we  have  a  Division  of  Forestry  of  the  Department  of  the 
Interior;  and  this  and  numerous  state  and  university  schools  of 
forestry  are  rapidly  teaching  the  people  of  this  country  the  best 
methods  for  the  preservation  of  our  forests.  The  Federal  Govern- 
ment has  set  aside  a  number  of  tracts  of  mountain  forest  in  some 
of  the  Western  states,  some  sixty  reserves  in  all,  making  a  total 
area  of  over  63,000,000  acres.  New  York  has  established  for  the 
same  purpose  the  Adirondack  Park,  with  nearly  1,500,000  acres 
of  timber  land.  Pennsylvania  has  one  of  700,000  acres,  and  many 
other  states  have  followed  their  example. 

Methods  for  Keeping  and  Protecting  the  Forests.  —  Forests 
should  be  kept  thinned.  Too  many  trees  are  as  bad  as  too  few. 
They  struggle  with  one  another  for  foothold  and  light,  which  only 
a  few  can  enjoy.  In  cutting  the  forest  it  should  be  considered 
as  a  harvest.  The  oldest  trees  are  the  '*  ripe  grain,"  the  younger 
trees  being  left  to  grow  to  maturity.  Several  methods  of  renewing 
the  forest  are  in  use  in  this  country.  (1)  Trees  may  be  cut  down 
and  young  ones  allowed  to  sprout  from  cut  stumps.  This  is  called 
coppice  growth.  This  growth  is  well  seen  in  parts  of  New  Jersey. 
(2)  Areas  or  strips  may  be  cut  out  so  that  seeds  from  neighboring 
trees  are  carried  there  to  start  new  growth.  (3)  Forests  may  be 
artificially  planted.  Two  seedlings  planted  for  every  tree  cut  is  a 
rule  followed  in  Europe.  The  greatest  dangers  are  from  fire  and 
from  careless  cutting,  and  these  dangers  may  be  kept  in  check  by 
the  efficient  work  of  our  national  and  state  foresters. 

A  City's  Need  for  Trees.  —  All  over  the  United  States  the 
city    governments    are    beginning    to    realize   what    European 


142 


OUR  FORESTS 


cities  have  long  known,  that  trees  are  of  great  value  to  a  city. 

Many  cities  are  spending  money  not  only  for  trees,  but  for 
proper  means  of  protection.  Thousands  of 
city  trees  are  annually  killed  by  horses, 
which  "  crib  "  upon  them.  This  may  be 
prevented  by  proper  protection  of  the 
trunk. 

Washington  spent  more  than  $37,000 
for  shade  trees  last  year;  Newark,  N.J., 
$27,000;  Springfield,  Mass.,  $21,500;  and 
St.  Louis,  $14,000.  Chicago  has  appointed 
a  city  forester,  who  has  given  the  following 
excellent  reasons  why  trees  should  be 
planted  in  the  city  :  — 

WM  (1)  Trees  are  beautiful  in  form  and  color, 

^K|  inspiring  a  constant  appreciation  of  nature. 

Hp[/  (2)  Trees  enhance  the  beauty  of  architecture. 

™-^  (3)  Trees  create  sentiment,  love  of  country, 

state,  city,  and  home. 

(4)  Trees  have  an  educational  influence  upon 
citizens  of  all  ages,  especially  children. 

(5)  Trees  encourage  outdoor  life. 

(6)  Trees  purify  the  air. 

(7)  Trees  cool  the  air  in  summer  and  radiate 
warmth  in  winter. 

(8)  Trees  improve  climate  and  conserve  soil  and  moisture 

(9)  Trees  furnish  resting  places  and  shelter  for  birds. 

(10)  Trees  increase  the  value  of  real  estate. 

(11)  Trees  protect  the  pavement  from  the  heat  of  the  sun. 

(12)  Trees  counteract  adverse  conditions  of  city  life. 

Let  us  all  try  to  make  Arbor  Day  what  it  should  be,  a  day  for 
caring  for  and  planting  trees,  for  thus  we  may  preserve  this  most 
important  heritage  of  our  nation. 


We  must  protect  our  city 
trees.  A  tree  badly- 
wounded  by  "  cribbing  " 
of  horses. 


Reference  Books 

elementary 

Sharpe,  A  Laboratory  Manual  for  the  Solution  of  Problems  in  Biology,    American 

Book  Company. 
Gofif  and  Mayne,  First  Principles  of  Agriculture.     American  Book  Company. 
Murrill,  Shade  Trees,  Bui.  205,  Cornell  University  Agricultural  Experiment  Station. 
Pinchot,  A  Primer  of  Forestry,  Division  of  Forestry,  U.S.  Department  of  Agriculture. 


OUR  FORESTS  143 


ADVANCED 

Apgar,  Trees  of  the  United  States,  Chaps.  II,  V,  VI.    American  Book  Company. 
Coulter,  Barnes,  and  Cowles,  A  Textbook  of  Botany,  Part  I  and  Vol.  II.     American 

Book  Company. 
Goebel,  Organography  of  Plants,  Part  V.    Clarendon  Press. 
Strasburger,  Noll,  Schenck,  and  Schimper,  A  Textbook  of  Botany.     The  Macmillan 

Company. 
Ward,  Timber  and  Some  of  its  Diseases.     The  Macmillan  Company. 
Yearbook,  U.S.  Department  of  Agriculture,  Division  of  Forestry,  Buls.  7,  10,  13,  16, 

17,  18,  20,  26,  27. 


XI.  THE  VARIOUS  FORMS  OF  PLANTS  AND  HOW  THEY 
REPRODUCE  THEMSELVES 

Problem  XX.    Some  forms  of  plant  life.    {Optional.)    {Labo- 
ratory Manual,  Proh.  XX.) 
{a)  An  alga, 
(jb)  A  fungus. 
(c)  A  moss, 
id)  A  fern. 

Simplest  Plant  Body  a  Thallus.  —  It  has  been  found  by  botanists 
that  the  plants  which  are  the  simplest  in  body  structure  are  those 
which  live  in  the  water.  Sometimes  such  simple  plants  are  found 
upon  rocks  or  on  the  bark  of  trees.  In  such  plants  we  can  distin- 
guish no  root,  stem,  or  leaf. 
The  plant  body  may  even  be 
spherical  in  outline  and  con- 
sist of  but  a  single  cell.  Such 
are  the  plants  (pleurococcus) 
which  give  the  green  color  to 
the  bark  of  trees.  Still  other 
plants  are  threadlike  in  ap- 
pearance.    Others,   as  sea- 

A  red  seaweed,   an  example  of  a  thallus  j        t_  mi  i  j 

1^^^  weeds,   have  a  ribbon-shaped 

body.  All  these  diverse  shapes 
of  plant  body  are  grouped  under  the  general  name  of  thallus.  The 
simplest  forms  of  plants  have  a  thalluslike  body. 

Adaptation  to  Environment.  —  Plants,  as  well  as  animals,  are 
greatly  affected  by  what  immediately  surrounds  them,  their  environ- 
ment. We  have  shown  in  our  experiments  that  the  environment 
(conditions  of  temperature,  moisture,  soil,  etc.)  is  capable  of  chang- 
ing or  modifying  the  structure  of  plants  very  greatly.  The  changes 
which  a  plant  or  animal  has  undergone,  that  jit  it  for  conditions  in 
which  it  lives,  are  called  adaptations  to  environment, 

144 


THE   VARIOUS   FORMS  OF   PLANTS 


145 


The  principal  factors  which  act  on  plants  and  which  make  up  their 
environment  are  soil,  water,  temperature,  and  light. 

The  first  plants  •  were  prol^ably  water-loving  forms.  It  seems 
likely  that,  as  more  land  appeared  on  the  earth's  surface,  plants 
became  adapted  to  changed  conditions  of  life  on  dry  land.  With 
this  change  in  habit  came  a  need  of  taking  in  water,  of  storing  it, 
of  conducting  it  to  various  parts  of  the  organism.  So  it  does  not 
seem  unlikely  that  plants  came  to  have  roots,  stems,  and  leaves,  and 
thus  became  adapted  to  their  environment  on  dry  land.  We  find 
in  nature  that  those  plants  or  animals  which  are  best  adapted  or 
fitted  to  live  under  certain  conditions  are  the  ones  which  survive 
or  drive  other  competitors  out  from  their  immediate  neighborhood. 
Nature  selected  those  which  were  best  fitted  to  live  on  dry  land, 
and  those  plants  eventually  covered  the  earth  with  their  progeny. 
Eventually,  the  forms  of  life  grew  more  and  more  complex  until 
at  last  very  complicated  organisms  such  as  the  flowering  plants 
came  to  live  upon  the  earth.  Between  the  flowering  plant  and 
the  simplest  of  all  plants  are  several  great  plant  groups  which  act 
as  steps  in  complexity  of  structure  between  the  most  lowly  and  the 
most  highly  specialized  plants. 
The  simplest  of  all  these  forms 
are  the  alga?. 

Algae.  —  The  algae  are  a  diverse 
collection  of  plants,  containing 
some  of  the  smallest  and  simplest 
as  well  as  some  of  the  largest 
plants  in  the  world.  The  tiny 
one-celled  plant  wliich  lives  on  the 
bark  of  trees  is  an  example  of  the 
former ;  the  giant  kelp  of  the  Pa- 
cific Ocean,  which  attains  a  length 
of  over  one  thousand  feet,  of  the 
latter.  The  body  of  the  algas  is 
a  thallus,  which  may  be  platelike, 
circular,  ribbon-formed,  thread- 
like, or  filamentous.  It  may  even 
be  composed  of  a  single  cell.     A 

large  number  of  the  algae  inhabit  the  water,  fresh  and  salt.  In  color  they 
vary  from  green  through  the  shades  of  blue-green  to  yellow,  brown,  and 
red.     The  latter  colors  are  best  seen  in  the  seaweeds,  all  of  wliich,   how- 

HUNT.  ES.  BIO.  — •  10 


A  red  seaweed,  showing  a  finely  divided 
thallus  body. 


146 


THE  VARIOUS  FORMS  OF  PLANTS 


ever,  contain  chlorophyll.  In  the  red  and  brown  seaweeds  the  chloro- 
phyll is  concealed  by  other  coloring  material  in  the  plant  body.  In  the 
olive-brown  fucus  (the  common  rockweed)  it  is  easy  to  prove  the  presence 
of  chlorophyll  by  cutting  open  the  bladders  which  are  found  in  the  plant 
body.  The  red  seaweeds  are  among  the  most  beautiful  and  delicate  of 
all  plants.  They  may  be  mounted  under  water  upon  cardboard  and 
then  studied  after  drying. 


Rockweed,  a  brown  alga,  showing  the  distribution  on  rocks  below  high-water  mark. 


Green  Algae.  —  The  plants  known  as  the  green  algse  are  of  more 
interest  to  us  because  of  their  distribution  in  fresh  water,  and 
also  beqause  of  their  economic  importance  as  a  supply  of  oxygen 
for  fish  and  other  animals  in  the  waters  of  our  inland  lakes  and 
rivers.  Our  attention  is  called  to  them  in  an  unpleasant  way  at 
times,  when,  after  multiplying  very  rapidly  during  the  hot  summer, 
they  die  rapidly  in  the  early  fall  and  leave  their  remains  in  our 
water  supply.  Much  of  the  unpleasant  taste  and  odor  of  drinking 
water  comes  from  this  cause. 

Pond  Scum  (Spirogyra).  —  This  alga  is  well  known  to  every 
boy  or  girl  who  has  ever  seen  a  small  pond  or  sluggish  stream.  It 
grows  as  a  slimy  mass  of  green  threads  or  filaments.  Frequently 
it  is  so  plentiful  as  almost  to  cover  the  surface  of  the  water,  buoyed 


THE   VARIOUS   FORMS   OF   PLANTS 


147 


up  by  little  bubbles  of  a  gas  which  seems  to  arise  from  the  body 
of  the  plant.  If  we  collect  some  of  this  gas,  we  can  easily  prove  that 
it  is  oxygen.     The  person  who  sees  a  pond  with  a  covering  of  slimy 


1 
1 

^      — > 

SI 

'«\ 

A,  jar  of  water  containing  pond  scum ;  B,  same  jar  after  an  hour  in  the  sunlight ; 
the  pond  scum  has  risen  to  the  top  of  the  jar,  buoyed  up  by  the  oxygen  formed 
within  it. 

pond  scum,  knowing  this  fact,  should  no  longer  feel  that  the  pond 
is  a  menace  to  health,  unless  it  is  a  place  where  mosquitoes  live  and 
breed. 
Under  the  low  power  of  the  microscope,  the  body  of  a  pond  scum 


Spirogyra :  n,  nucleus ;  s,  chlorophyll  bands. 

is  seen  to  be  a  thread  made  up  of  elongated  cylindrical  cells,  each 
of  which  contains  a  spirally  wound  band  of  chlorophyll  within  it. 


148 


THE  VARIOUS   FORMS  OF  PLANTS 


Careful  study  shows  the  presence  of  strands  held  in  the  body  of 
the  cell  by  strands  of  protoplasm,  the  remainder  of  the  space 
within  the  cell  being  occupied  by  the  cell  sap. 

Pond  scum  may  grow  by  a  simple  division  of  the  cells  in  a  fila- 
ment. This  method  of  asexual  reproduction  is  the  way  growth 
takes  place  in  the  cells  of  the  root,  stem,  or  leaf  of  a  flowering 
plant,  but  another  method  of  reproduction  is  also  seen  in  pond 
scum.  The  cells  of  two  adjoining  filaments  may  push  out  tubes 
which  meet,  thus  connecting  the  cells  with  each 
other.  Meantime  the  protoplasm  of  the  cells 
thus  joined  condenses  into  two  tiny  spheres ;  the 
bands  of  chlorophyll  are  broken  down,  and  ulti- 
mately the  contents  of  one  of  the  cells  passes  over 
the  tube  and  mingles  with  the  cell  of  the  neigh- 
boring filament,  with  which  it  was  previously  con- 
nected by  the  tube  formed  from  the  cell  walls. 
The  result  of  this  process  of  fusion  is  a  thick- 
walled  resting  cell  which  we  call  a  zygospore. 

Conjugation.  —  The  process  in  which  two  cells 
of  equal  size  unite  to  form  a  single  cell  is  called 
conjugation.  It  is  believed  to  be  a  sexual  process 
which  corresponds  in  a  way  to  the  fertihzation 
in  the  higher  plants.^  This  cell  thus  formed  can 
withstand  considerable  extremes  of  heat  and  cold, 
and  may  be  dried  to  such  an  extent  that  it  is 
found  in  dust  or  in  the  air.  Under  favorable 
conditions,  this  spore  will  germinate  and 
produce  a  filament. 

Pleurococcus.  —  Many  other  forms  of  algse 

are  well  known  to  us.     One  of  the  simplest  is  ^^-^'--^  r 

pleurococcus.      This  httle  plant  consists  of  a  pieurococcus.    ^.single  cell; 

smgle  tmy  cell,  which  by  division  may  give  b,  colony  of   four  cells 

rise  to  two,  three,  four,  or  even  more  cells  formed   from    the    original 

which  cling  together  in  a  mass.     The  green  cell  A. 

^  Material  which  shows  conjugation  is  not  always  easy  to  obtain.  Conjugation 
usually  takes  place  most  freely  in  the  fall  of  the  year.  When  material  is  obtained, 
it  may  be  preserved  in  a  4  per  cent  solution  of  formol.  Material  killed  in  a  5  per 
cent  solution  of  chromic  acid  and  then  preserved  in  70  per  cent  alcohol  or  4  per 
cent  formol  shows  the  details  of  cellular  structure. 


Conjugation  of 
Spirogyra;  zs, 
zygospore;  /, 
fusion  in  progress. 


THE   VARIOUS  FORMS   OF  PLANTS 


149 


color  on  tree  trunks,  stone  houses,  etc.,  is  due  to  millions  of  these  little 
plants. 

Diatoms.  —  These  plants  are  found  in  vast  numbers  living  on  the  mud 
or  stones  at  the  bottom  of  small  streams.     The  plant  body  is  inclosed  in 
a  cell  wall  composed  largely  of  silica.     Many  of 
the    diatoms   are    free-swimming.     They    compose 
a  large  percentage  of  the  living  organisms  found 
near  the  ocean's  surface. 

Diatoms  are  found  as  fossils,  and  make  up  a  large 
proportion  of  many  rocks.  The  siliceous  skeletons 
in  such  rocks  are  of  commercial  importance,  the 
rock  forming  a  basis  for  polishing  powders. 


Various  forms  of  Di- 
atoms. 


Fungi,  Parasites,  and  Saprophytes.  —  The 
thallus  plants  may  be  grouped  in  two  great 
divisions:  the  Alg(£,  water-loving  ihallophytes 
containing  chlorophyll,  and  the  Fungi,  thallus 
plants  which  do  not  contain  chlorophyll.  As  a 
direct  result  of  the  lack  of  chlorophyll  in  the 
cells,  the  fungi  are  unable  to  make  their  own 
food.  They  must  obtain  food  from  other  plants 
or  animals.  Some  take  up  their  abode  upon  living  plants  or  ani- 
mals {in  which  case  they  are  called  parasites) ;  others  obtain  their  food 
from  some  dead  organic  matter.     The  latter  are  called  saprophytes. 

The  above  facts  make  the 
group  of  the  fungi  of  immense 
economic  importance  to  man. 

Mold  {Rhizopus  nigricans). — 
One  of  the  most  common  of  all 
our  fungi  is  the  black  mold 
which  appears  growing  upon 
bread,  cake,  and  other  organic 
substances  under  certain  con- 
ditions of  temperature  and 
moisture. 

The  tangled  mass  of  threads  which  cover  the  bread  is  called  the 
mycelium,  each  thread  being  called  a  hypha.  Many  of  the  hyphse 
are  prolonged  into  tiny  upright  threads,  bearing  at  the  top  a  httle 
ball.  With  the  low  power  of  the  microscope  each  of  these  struc- 
tures is  seen  to  contain  many  tmy  bodies  called  spores.    These 


Bread  mold  :  r,  rhizoids  ;  s,  sporangium. 


150 


THE  VARIOUS  FORMS  OF  PLANTS 


spores  have  been  formed  by  the  division  of  the  protoplasm  mak- 
ing up  the  ball  or  sporangium  into  many  separate  bodies. 

This  method  of  the  production  of  spores  is  evidently  asexual. 
These  spores,  if  grown  under  favorable  conditions,  will  produce 
more  mycelia,  which  in  turn  bear  sporangia.  It  has  been  found, 
however,  that  at  some  time  during  the  life  of  the  mold  another 
method  of  reproduction  is  likely  to  occur. 

Formation  of  Zygospores.  —  Two  hj^hse  which  are  close-lying 
put  out  threads  which  communicate.     The  end  of  each  of  the 

threads  cuts  off  a  cell,  and  the  two 
cells,  each  from  a  different  hypha,  flow 
together  and  mingle.     In  this  condi- 
tion they  remain  as  a  single  resting 
cell.     This  cell,   which  puts  a  heavy 
D  wall    around    itself,    is    a    zygospore. 
Here  again  we  have  a  process  of  con- 
jugation similar  to  that  we  observed 
in  the  pond  scum.     The  ultimate  re- 
sult of  the  conjugation  of  the  two  cells 
is  that  a  new  plant  grows  from  the 
zygospore  after  a  period  of  rest.     Dur- 
ing the  resting  stage  the  spore  may 
undergo  very  unfavorable  conditions, 
even  to  extreme  dryness,  heat,  or  cold. 
Conjugation  of  black  mold :  A,  The  use  of  the  zygospore  to  the  plant 
B,  c,  D,  successive  stages  in  jg  evidently  to  Continue  the  species 
the  formation  of  the  zygospore,   ^^^.j^^  ^^  unfavorable  time  in  the  Hfe 

history  of    the  plant.     The   process  of    conjugation  is  probably 
a  sexual  process,  as  we  have  called  it  in  pond  scum. 

Physiology  of  the  Growth  of  Mold.  —  Mold,  in  order  to  grow 
rapidly,  evidently  needs  oxygen,  moisture,  and  heat.  It  obtains 
its  food  from  the  material  on  which  it  lives.  This  it  is  able  to 
do  by  means  of  digestive  ferments  which  are  given  out  by  the 
rhizoids  or  rootlike  parts  of  the  hyphse,  by  means  of  which  the 
mold  clings  to  the  bread.     These  ferments  change  the  starch  of 


1  It  seems  to  have  been  proved  recently  that  zygospores  are  formed  by  the  union 
of  two  cells,  from  different  filaments,  one  of  which  has  male,  the  other  female,  char- 
acters. 


THE   VARIOUS   FORMS   OF   PLANTS 


151 


the  bread  to  sugar  and  the  proteid  to  a  soluble  form  which  will 
pass  by  osmosis  into  the  hypha?.  Thus  the  plant  is  enabled  to 
absorb  the  material.  This  food  is  then  used  to  supply  energy  and 
make  protoplasm.  This  seems  to  be  the  usual  method  by  which 
saprophytes  assimilate  the  materials  on  which  they  live. 


Other  Saprophytic  Fungi.  —  The  mushroom  resembles  a  tiny  umbrella. 
The  upper  part  is  known  to  botanists  as  the  cap ;  the  cap  is  held  up  by  a 
stalk  or  stipe.  The  under  surface  of  the  cap  discloses  a  number  of  struc- 
tures which  radiate  out  from 
the  central  stipe  to  the  edge  of 
the  cap.  These  are  the  gills. 
If  you  place  the  cap  of  a  mush- 
room gills  downward  on  the 
surface  of  a  piece  of  white 
paper,  being  careful  not  to  dis- 
turb for  at  least  twelve  hours, 
it  will  be  found  that  when  tho 
cap  is  removed  a  print  of  the 
shape  and  size  of  the  gills  re- 
mains on  the  paper.  This  is  a 
spore  print.  It  has  been  caused 
by  the  spores  of  the  plant,  which 
have  fallen  from  the  place  where 
they  were  formed  between  the 
gills  to  the  surface  of  the  paper. 

Mycelium.  —  The  mushroom 
is,  then,  the  spore-bearing  part 
of  the  plant.  Where  is  the  plant 
body?  This  question  is  an- 
swered if  we  dig  up  a  little  of 
the  earth  surrounding  a  mush- 
room. In  the  rich  black  soil  is 
seen   a    mass   of   little    whitish 

threads.  These  tlu-eads  form  the  mycelium  of  the  fungus.  The  hyphse 
of  this  part  of  the  plant  body  take  food  from  the  organic  matter  in  the 
soil  and  digest  it  in  the  same  manner  as  did  the  hyphas  of  black  mold. 
The  mushroom  is  a  saprophyte.    No  sexual  stage  has  yet  been  discovered. 

Food  Value  of  Mushrooms.  —  The  food  value  of  the  edible  mushroom 
has  been  much  overestimated.  Recent  experiments  seem  to  show  that, 
although  they  have  a  sUght  food  value,  they  are  far  from  taking  the  place 
of  nitrogenous  foods,  as  was  formerly  believed  by  scientists. 

Other  Fungi.  — Many  other  plants,  both  useful  and  harmful  to  man, 
belong  in  this  group ;  among  them  are  the  yeasts,  the  various  parasitic 


Mushrooms ;  the  younger  specimen,  at  the 
right,  shows  the  mycehum.  Photographed 
by  Overton. 


152 


THE  VARIOUS  FORMS  OF  PLANTS 


rusts  and  smuts,  causing  plant  diseases,  and,  most  important  of  all,  the 
bacteria.  We  shall  consider  several  of  these  plants  later  in  their  direct 
relation  to  the  human  race. 

Mosses 


Mosses  are  mostly  shade-loving  and  moisture-loving  plants.  They 
form  velvety  carpets  in  many  of  our  forests,  but  they  often  show  their 
preference  for  moist  localities  by  covering  the  wooded  shores  of  lakes 
and  swamps. 

Pigeon-wheat  Moss.  —  One  of  the  mosses  frequently  seen  and  easily 
recognized  i^  the  so-called  pigeon- wheat  moss   {Polytrichum  commune). 

Unlike  some  mosses,  it  often  inhabits  dry 
localities.  It  may  be  found  on  some  dry 
hillock  close  to  the  edge  of  the  woods, 
where  it  forms  a  reddish  brown  carpet. 
This  red  color  is  due  largely  to  the  pres- 
ence of  a  great  number  of  little  upright 
stalks,  bearing  at  the  summit  tiny  cap- 
sules, which  seem  to  grow  up  from  the 
leafy  moss  plant.  The  resemblance  of  a 
large  number  of  these  stalks  and  capsules 
to  a  mimic  field  of  grain  has  given  the 
name  pigeon- wheat  moss  to  this  form. 

Forms  of  Plants.  —  Three  kinds  of 
moss  plants  appear  to  be  present :  leafy 
plants,  others  bearing  a  stalk  and  cap- 
sule, and  still  others  which  terminate  at 
the  end  in  a  little  rosette  of  leaves,  in- 
closing what  appears  to  be  a  tiny  flower. 
Leafy  Moss  Plant.  —  A  leafy  moss 
plant  has  rhizoids  or  hairlike  roots,  an 
upright  stem,  and  green  leaves.  In  the 
plants  which  have  a  stalk  and  capsule, 
the  stalk  grows  directly  from  the  end  of 
the  leafy  plant.  This  capsule  is  provided 
with  an  outer  cap  which  seems  to  have 
somewhat  the  structure  of  a  thatched 
roof.  Under  the  cap  is  found  a  lid,  or 
cover,  to  the  capsule.  If  this  cover  is 
removed  and  the  capsule  turned  upside 
down,  the  dust  that  escapes  will  be  found 
to  be  made  up  of  a  great  number  of  spores. 
Sporophyte.  —  The  capsule  is  the 
spore-producing  part  {sporangium)  of  the  moss  plant.  The  stalk  and  cap- 
sule together  form  the  sporophyte  or  spore-producing  generation  of  the  moss. 


Two  moss  plants,  showing  the 
gametophyte  (G)  and  the  sporo- 
phyte iS). 


THE   VARIOUS   FORMS   OF  PLANTS  153 

If  we  were  to  plant  the  spores  of  the  moss  in  damp  sand,  taking  care  to 
keep  the  sand  moist  and  warm,  we  might  get  them  to  grow.  The 
spore  germinates  into  a  threadlike  structure,  very  tiny,  and  not  at  all 
like  the  adult  moss  j)lant.     This  thread  is  called  a  prolonema. 

Adult  Moss  Plants.  —  The  protonema  soon  develops  rhizoids ;  tiny 
buds  appear  which  in  time  form  the  adult  moss  j)lant.  These  adult  plants 
may  grow  only  leaves,  and  become  what  are  known  as  sterile  plants;  or 
they  may  develop  into  a  plant  that  bears  at  the  summit  the  little  ro?ette 
of  leaves  previously  referred  to.  Within  the  rosette  lie  a  number  of  tiny 
organs  which  hold  large  numbers  of  sperm  cells.  Other  moss  plants  not 
so  tall  as  the  sperm-producing  plants  bear  at  the  summit  of  the  stem  a 
tuft  of  leaves  which  hide  a  number  of  small  flask-shaped  structures,  each 
of  which  contains  a  single  egg  cell.  These  pUints  form  the  sexual  genera- 
tion of  the  moss.  This  stige  of  the  -plant  is  called  the  gametophyte,  because 
it  produces  the  gametes  or  sexual  cells,  —  eggs  and  sperms.  After  a  sperm 
cell  has  been  transferred  (usually  by  means  of  a  drop  of  dew)  to  the  egg 
cell,  a  fusion  of  the  two  cells  takes  place.  This,  we  remember,  is  the  pro- 
cess of  fertilization.  In  the  mosses  the  fertilization  of  the  egg  cell  results 
in  the  growth  of  that  part  of  the  plant  which  forms  and  bears  the  asexual 
spores. 

Alternation  of  Generations.  —  In  the  mosses  we  have  what  is  known 
as  an  alternation  of  generations.  The  leafy  moss,  bearing  among  its  leaves 
the  organs  producing  sperms  and  eggs,  antheridia  and  archegonia,  gives 
place  to  a  stalk  and  capsule  bearing  the  asexual  spores.  This  spore-bear- 
ing portion  of  the  plant  does  not  appear  until  after  fertilization ;  then  it 
grows  directly  out  of  that  part  of  the  plant  which  produces  the  egg  cell. 
In  fact,  if  we  make  a  microscopic  examination  of  the  egg-producing  struc- 
ture (the  archegonium)  directly  after  fertilization,  we  find  that  the  sporo- 
phyte  is  a  direct  outgrowth  from  the  fertilized  egg  cell.  Thus  the  sexual 
stage  alternates  with  the  asexual  stage  in  the  life  of  the  plant. 

Sporophyte  a  Parasite.  —  One  interesting  fact  comes  out  in  connection 
with  this  growth  of  the  sporophyte.  It  has  no  green  leaves  and  must 
therefore  obtain  all  its  nourishment  from  the  leafy  moss  plant,  or  game- 
tophyte. The  spore-bearing  part  of  the  plant  is  thus  actually  a  parasite 
upon  the  gametophyte. 


Ferns  and  their  Allies 

The  Ferns  and  their  Allies.  —  The  fern  plants  include  the  true  ferns, 
the  horsetails  or  scouring  rushes,  and  the  club  mosses.  The  true  ferns 
are  moisture-loving  and  shade-loving  plants  ;  they  play  an  important  part 
in  the  vegetation  of  the  tropical  forests.  Many  forms  are  found  in  the 
temperate  regions ;  we  even  have  some  common  ferns  that  remain  green 
all  winter.  Fossil  ferns  have  been  found  in  Greenland,  thus  showing  that 
at  one  time  the  climate  at  the  north  was  milder  than  it  now  is. 


154 


THE   VARIOUS   FORMS  OF  PLANTS 


A  common  fern  is  the  polypody  (Polypodium  vulgare),  the  habitat 
of  which  is  damp  woods  and  rocky  glens.  These  ferns  are  hard  to  pro- 
cure entire,  as  they  have 
an  underground  stem,  from 
which  at  intervals  the  leaves 
or  fronds  arise.  The  leaflets 
or  pinnce  at  certain  seasons 
show  a  series  of  little  brown 
dots  on  the  under  surface. 
These  structures,  called  col- 
lectively the  sori  (singular 
sorus),  are  made  up  of  a 
number  of  tiny  spore  cases. 
These  spore  cases,  or  sporan- 
gia, hold  the  asexual  spores. 
These  spores  under  favorable 
conditions  of  heat  and  mois- 
ture may  germinate  to  form  a 
tiny  thread  of  cells  which 
soon  develops  into  a  flat, 
heart-shaped  body  not  much 
bigger  than  a  pinhead,  called 
a  prothallus. 

Prothallus.  —  The  pro- 
thallus clings  to  the  surface 
of  the  ground  by  means  of  its 
rhizoids.  A  careful  examina- 
tion of  the  prothallus  with  a  compound  microscope  reveals  the  fact  that 
scattered  among  the  rhizoids  are  some  tiny  rounded  elevations ;  immedi- 
ately above  the  rhizoids  and  between  them  and  the  little  groove  (see  Fig- 
iu*e)  in  the  prothallus  are  other  structures ;  both  the  above  structures 
are  too  minute  to  find  with  the  naked  eye. 

Archegonia.  —  The  last  named  are  archegonia;  they  are  found  to  be 
very  tiny  flask-shaped  organs  almost  embedded  in  the  surface  of  the 
prothallus.  Each  archegonium  contains  a  single  large  egg 
cell. 

Antheridia.  —  The  other  structures  found  among  the 
rhizoids  are  the  antheridia.  Each  antheridium  contains  a 
large  number  of  very  minute  objects  which  are  able  to 
move  about  in  water  by  means  of  lashlike  threads  of  pro- 
toplasm. Each  of  these  motile  cells  is  called  an  antherozoid ; 
they  have,  in  fact,  the  'same  function  as  the  sperm  cells  of 
the  flowering  plants.  Because  this  part  of  the  plant  holds 
the  egg  cells  and  sperm  cells,  we  recognize  it  as  the  sexual  generation  of 
the  fern. 


Rock  fern,  polypody.  Notice  the  underground 
stem  giving  off  roots  {R)  from  its  under  sur- 
face, and  leaves  (C)  from  the  upper  surface. 
The  compound  leaf  or  frond  may  bear  sori 
(<S)  on  the  underside  of  the  leaflets. 


A  sporangium. 


THE   VARIOUS   FORMS  OF  PLANTS 


155 


ap. 


an-.\^,^ 


Prothalium  of  a  common  fern  (aspidium)  : 
A,  under  surface,  showing  rhizoids,  rh, 
anthcridia,  an,  and  archegonia,  ar;  B, 
under  surface  of  an  older  gametophyte, 
showing  rhizoids,  rh,  and  young  spo- 
rophyte,  with  root,  w,  and  leaf,  b.  (From 
Coulter,  Plant  Structures.) 


Fertilization.  —  The  sperm  cells  swim  to  the  egg  cells  in  water  (rain  or 
dew),  being  attracted  to  the  mouth  of  the  flask-shaped  archegonium  by 
an  acid  secretion  which  is  poured  out  by  the  cells  forming  the  neck  of  the 
flask.     Fertilization  is  essentially 
the  same    process   that  has  been 
described  for  the  flowering  plants, 
the   sperm  cell  uniting   with   the 
egg  cell  to  form  a  single  cell,  the 
fertilized  egg. 

Sporophyte  and  Gametophyte. 
—  The  direct  result  of  fertilization 
is  the  growth  of  the  egg  cell  by  re- 
peated division  to  form  a  little 
fern  plant.  Later  the  young  plant 
strikes  root,  the  prothallus  dies 
away,  and  we  have  a  fern  plant 
which  will  later  in  the  season  pro- 
duce asexual  spores.  The  leafy 
fern  plant,  because  it  produces 
asexual  spores,  is  called  the  sporo- 
phyte. The  prothallus,  which  forms 
the  eggs  and  sperms,  both  of  which 
are  known  as  gmnetes,  or  sex  cells,  is  called  the  gametophyte. 

Alternation  of  Generations.  —  The  fern  plant  like  the  moss  also  passes 
through  two  entirely  different  stages,  or  generations.  The  spore  ger- 
minates to  form  a  gametophyte,  or 
sexual  generation.  This  sexual 
generation  in  turn  produces  an 
asexual  generation,  or  sporophyte. 
The  alternation,  in  the  life  history  of 
a  plant  or  animal,  of  a  sexual  stage 
with  an  asexual  stage  is  called  an 
alternation  of  generations. 

General  Characters  of  the  Fern- 
like Plants.  —  These  plants  pass 
through  an  alternation  of  genera- 
tions; they  have  a  distinct  root, 
stem,  and  leaves;  and  the  stem 
possesses  conducting  tubes  or  fibro- 
vascular  bundles;  these  are  the 
distinguishing  marks  of  the  ferns  and  their  allies.  Fern  plants  show  a 
great  diversity  in  form  and  size.  They  vary  from  the  great  tree  ferns  of 
the  tropics,  some  of  which  are  thirty  to  forty  feet  in  height,  to  tiny  forms 
of  almost  microscopic  size.  The  leaves  of  the  ferns  are  among  the  most 
complex  in  form  of  any  that  we  know. 


B  A 

A,  the  archegonlum  with  egg  (e)  and  canal 
(c)  ;  B,  antheridium  ;  C,  antherozoid, 
very  highly  magnified.  —  Strasburger. 


156  THE  VARIOUS  FORMS  OF  PLANTS 

The  Horsetails.  —  These  comprise  a  small  group  of  plants,  recognized 
by  their  erect  habit  of  growth,  the  leaves  coming  out  in  whorls  on  the  stem. 
In  most  forms  the  stem  contains  considerable  silica.  This  gave  to  the 
plant  its  former  useful  place  in  the  household  and  its  name  of  the  scour- 
ing rush.  If  you  burn  one  of  these  plants  very  carefully  on  a  tin  plate  over 
a  very  hot  fire,  the  delicate  skeleton  of  silica  may  be  seen.  The  horse- 
tails, or  Equisetums,  were  once  a  very  important  part  of  the  earth's 
vegetation.  Before  the  coal  fields  were  formed,  the  ancestors  of  these 
plants  flourished  as  trees.  A  large  amount  of  the  coal  of  this  country  is 
undoubtedly  formed  from  the  trunks  of  the  Equisetums  of  the  Carbonif- 
erous age.  At  present  they  are  represented  by  a  very  few  species,  none 
of  which  are  over  four  or  five  feet  in  height. 

Club  Mosses.  —  Another  relative  of  the  fern  is  the  club  moss  (lyco- 
podium).  It  is  familiar  to  us  as  a  Christmas  decoration  under  the  name 
of  ground  pine.  It  is  chiefly  of  interest  now  as  the  representative  of 
another  group  of  plants  that  flourished  during  the  Carboniferous  age. 

Economic  Value  of  Ferns.  —  It  may  be  said  that  the  ferns  as  a  group 
have  formed  a  large  part  of  the  enormous  deposits  of  almost  pure  carbon 
that  we  call  coal,  from  which  we  now  derive  the  energy  to  run  our  many 
engines. 

Sexual  Reproduction  in  Flowering  Plants.  —  Flowering  plants 
reproduce  their  kind  by  the  formation  of  seeds.  As  we  know,  the 
flower  produces  in  the  ovary  structures  which  are  known  as  omiles. 
In  the  interior  of  the  ovule  is  found  a  clear  protoplasmic  area  which 
is  called  the  embyro  sac.  In  this  area  is  a  cell  (the  egg  cell)  which 
is  destined  to  form  the  future  plant.  In  the  pollen  grain  is  found 
another  cell,  the  sperm.  This  cell,  after  the  germination  of  the 
pollen  grain  on  the  stigmatic  surface  of  the  flower,  enters  the  ovule 
in  the  pollen  tube  and  unites  with  the  egg  cell.  The  fertiHzed  egg 
grows  into  the  young  plant  within  the  seed,  known  as  the  embryo 
(see  page  37). 

This  method  of  reproduction,  called  sexual  reproduction,  is 
found  in  the  spermatophytes,  that  is,  all  seed-producing  plants. 

Botanists  have  shown  that  in  the  spermatophytes  there  exists 
an  alternation  of  generations  as  in  the  mosses  and  ferns.  The 
pollen  grain  is  believed  to  contain  the  male  gametophyte,  while 
within  the  embryo  sac  is  found  the  female  gametophyte.  Most  of 
the  Hfe  of  the  flowering  plant  is  thus  seen  to  be  passed  in  the  asexual 
or  sporophyte  stage.  Thus  we  see  that  all  plants  —  and  all  ani- 
mals as  well  —  form  the  cells  which  compose  their  bodies  by  either 


THE  VARIOUS  FORMS  OF  PLANTS  157 

sexual  or  asexual  growth,  and  the  stage  of  asexual  growth  is  usually 
separated  from  the  period  of  sexual  growth. 

Systematic  Botany.  —  The  plant  world  is  divided  into  many 
tribes  or  groups.  And  not  only  are  plants  placed  in  large  groups 
which  have  some  very  conspicuous  characters  in  common,  but 
smaller  groupings  can  be  made  in  which  perhaps  ordy  a  few  plants 
having  common  characters  ma}'  be  placed.  If  we  plant  a  number  of 
peas  so  that  they  will  all  germinate  under  the  same  conditions  of 
soil,  temperature,  and  sunlight,  the  seedlings  that  develop  will  each 
differ  one  from  another  in  a  slight  degree.  But  in  a  general  way 
they  will  have  many  characters  in  common,  as  the  shape  of  the 
leaves,  the  possession  of  tendrils,  form  of  the  flower  and  fruit. 
The  smallest  group  of  plants  or  animals  having  certain  characters  in 
common  that  make  them  different  from  all  other  plants  or  animals  is 
called  a  species.  Individuals  of  such  species  differ  slightly;  for 
no  two  individuals  are  exactly  alike. 

Species  are  grouped  together  in  a  larger  group  called  a  genus. 
For  example,  many  kinds  of  peas  —  the  garden  peas,  the  wild 
beach  peas,  the  sweet  peas,  and  many  others  —  are  all  grouped  in 
one  genus  (called  LathyniSj  or  vetchling)  because  they  have  certain 
structural  characteristics  in  common. 

Plant  and  animal  genera  are  brought  together  in  still  larger 
groups,  the  classification  based  on  general  likenesses  in  structure. 
Such  groups  are  called,  as  they  become  successively  larger.  Family, 
Order,  and  Class.  Thus  the  whole  plant  and  animal  kingdom  is 
grouped  into  divisions,  the  smallest  of  which  contains  individuals 
very  much  alike ;  and  the  largest  of  which  contains  very  many 
groups  of  individuals,  the  groups  having  some  characters  in  com- 
mon.    This  is  called  a  system  of  classification. 

Classification  of  the  Plant  Kingdom.  —  The  entire  plant  king- 
dom has  been  grouped  as  follows  by  botanists :  — 

-     cr  J     1   J       \  Angiosperms,  true  flowering  plants. 

1.  bpermatophytes.  ]  ^  '     ,       .  ,    ,    .      „. 

[  Gymnosperms,  the  pmes  and  their  allies. 

2.  Pteridophytes.     The  fern  plants  and  their  allies. 

3.  Bryophytes.     Moss  plants  and  their  allies. 

4.  Thallophytes.  The  Thallophytes  form  two  groups :  the  Alga? 
and  the  Fungi. 

The  extent  of  the  plant  kingdom  can  only  be  hinted  at,  because 


158  THE  VARIOUS  FORMS   OF  PLANTS 

each  year  new  species  are  added  to  the  hsts  There  are  about 
110,000  species  of  flowering  plants  and  nearly  as  many  flowerless 
plants.  The  latter  consist  of  over  3500  species  of  fernlike 
plants,  some  16,500  species  of  mosses,  over  5600  lichens  (plants 
consisting  of  a  partnership  between  algai  and  fungi),  approxi- 
mately 55,000  species  of  fungi,  and  about  16,000  species  of  algae. 

Rbferkncb  Books 

elementary 

Sharpe,  A  Laboratory  Manual  for  the  Solution  of  Problems  in  Biology.    American 

Book  Company. 
Andrews,  Botany  All  the  Year  Round,  Chap.  X.     American  Book  Company. 
Atkinson,  Lessons  in  Botany,  Chaps.  Ill,  XIX-XXIX.    Ginn  and  Company. 
Conn,  Bacteria,  Yeasts,  and  Molds  in  the  Home.     Ginn  and  Company. 
Coulter,  Plant  Stuxlies,  Chaps.  XVII,  XXIV.     D.  Appleton  and  Company. 
How  to  Grow  Mushrooms,  Bui.  53,  U.S.  Department  of  Agriculture. 
Mushroom  Poisoning,  Cir.  13,  U.S.  Department  of  Agriculture. 
Parsons,  How  to  Know  the  Ferns.     Charles  Scribner's  Sons. 

ADVANCED 

Atkinson,  Mushrooms,  Edible  and  Poisonous.     Andrews  and  Church. 

Bergen  and  Davis,  Foundations  of  Botany  (Cryptogamic  portion).  Ginn  and  Com- 
pany. 

Coulter,  Barnes,  and  Cov/les,  A  Textbook  of  Botany,  Vol.  I.  American  Book  Com- 
pany. 

De  Bary,  Comparative  Anatomy  of  Phanerogams  and  Ferns.    Clarendon  Press. 

De  Bary,  Comparative  Morphology  and  Biology  of  the  Fungi,  Mycetozoa,  and  Bacteria. 
Clarendon  Press. 

Goodale,  Physiological  Botany.     American  Book  Company. 

Grout,  Mosses  with  a  Hand  Lens.     A.  J.  Grout. 

Leavitt,  Outlines  of  Botany.     American  Book  Company. 

Marshall,  The  Mushroom  Book.     Doubleday,  Page,  and  Company. 

Sedgwick  and  Wilson,  General  Biology.     Henry  Holt  and  Company. 

Strasburger,  Noll,  Schenck,  and  Schimper,  A  Textbook  of  Botany.  The  Macmillan 
Company. 

Underwood,  Our  Native  Ferns  and  their  Allies.     Henry  Holt  and  Company. 

Underwood,  Molds,  Mildews,  and  Mushrooms.     Henry  Holt  and  Company. 

Yearbook,  U.S.  Department  of  Agriculture,  1894,  1897,  1900. 


XII.   HOW  PLANTS   ARE  MODIFIED   BY  THEIR  SUR- 
ROUNDINGS 

Problem  XXI.    How  plants  are  niodifled  by  tlieir  surround- 
ings.   {Oj)tional).    {.Laboratonj  Manual,  Frob.  XXI. ^ 

(a)  Hydrophytic  society. 

(b)  Xerophytie  society. 

(c)  Mesophyti<i  socisty. 

(d)  Plant  societies. 

(e)  Plant  zonation. 

The  Way  in  which  Plants  are  Modified  by  their  Surroundings.  — 
As  we  have  found  in  our  experiments,  young  plants,  and  indeed 
any  living  plants,  are  delicate  organisms,  which  are  affected  pro- 
foundly by  the  action  of  forces  outside  themselves.  The  presence 
or  absence  of  moisture  starts  or  prevents  growth  in  seeds  or  young 
plants ;  absence  of  light  changes  the  form  and  color  of  green  plants ; 
a  certain  temperature,  which  varies  for  different  plants,  seems  to  in- 
fluence plants  in  a  healthy 
growth.  Pea  seedlings 
may  grow  for  a  time  in 
sawdust,  but  we  know  that 
they  will  be  much  healthier 
and  will  live  longer  if 
allowed  to  germinate  in 
soil  under  natural  condi- 
tions. We  are  forced  to 
the  conclusion  that  differ- 
ences in  the  form  and 
habits  of  plants  are  caused 
by  the  action  of  their  sur- 
roundings upon  them. 
The  plants  which  have  be-    „     ,  ,.,.       ,    ,      ,,  „     .     , 

^  ^  Poncl  lihcs,  phuit.s  with  floatiiin  Icaxc; 

come  in  various  ways  fitted  graph  by  W.  C.  Barbour. 

159 


Photo- 


160    PLANTS  MODIFIED  BY  THEIR  SURROUNDINGS 


to  live  under  certain  conditions  are  said  to  be  adapted  to  live  under 
such  conditions.  Such  plants  as  are  best  fitted  to  live  under  certain 
conditions  are  the  ones  which  will  survive. 

Water  Supply.  —  Water  supply  is  one  of  the  important  factors 
in  causing  changes  in  structure  of  plants.  Plants  which  live  en- 
tirely in  the  water,  as  do  many  of  the  algie,  have  slender  parts, 
stemlike,  and  yet  serving  the  place  of  a  leaf.  The  interior  of  such 
a  plant  is  made  up  of  spongy  tissues  which  allow  the  air  dissolved 
in  the  water  in  which  they  live  to  reach  all  parts  of  the  plant. 

If  the  plant  has  floating  leaves,  as 
in  the  pond  lily,  the  stomata  are 
all  in  the  upper  side  of  the  leaf. 

Plants  living  in  water  have  not  only 
loose  and  spongy  tissues,  but  many 
large  intercellular  spaces  are  found  in 
stems  or  leaves.  In  one  pond  lily 
( Nelumbo  lutea)  these  spaces  in  the 
leaf  communicate  with  large  spaces 
in  the  veins  of  the  leaf,  and  these  in 
turn  with  spaces  in  the  petiole,  stem, 
and  root,  so  that  all  parts  of  the 
plants  are  in  communication  with  the 
air  above.  The  roots  of  a  plant  living 
wholly  in  water  are  not  needed  for 
support,  hence  they  are  often  short 
and  stumpy.  They  do  not  need  to 
be  modified  to  absorb  water;  conse- 
quently the  absorbing  surface  lacks 
root  hairs.  The  whole  plant,  when  under  water,  is  usually  modified  to 
take  water  and  material  used  in  food-making  from  its  immediate  environ- 
ment. 

Hydrophytes.  —  If  water  is  present  in  such  quantity  as  to  satu- 
rate the  soil  in  which  the  plant  lives,  the  conditions  of  its  environ- 
ment are  said  to  be  hydrophijtic,  and  such  plant  is  said  to  be  a  hydro- 
phyte. 

Xerophytes.  —  If  we  examine  plants  growing  in  dry  or  desert 
conditions,  as  cactus,  sagebrush,  aloe,  etc.,  we  find  that  the  leaf 
surface  is  invariably  reduced.  Leaves  are  reduced  to  spines  in 
the  cactus.  Some  plants,  such  as  the  three-angled  spurge,  which 
bear  leaves  in  a  condition  of  moderate  water  supply,  take  on  the 


A   water    plant,    showing   the   finely 
divided  leaflike  parts. 


PLANTS  MODIFIED   BY  THEIR  SURROUNDINGS    161 

appearance  of  a  cactus  under  desert  conditions.  Thus  thej^  lose 
their  evaporating  leaf  surface  by  having  the  leaves  changed  into 
spines. 

The  stem  may  be  thickened  so  as  to  store  water ;   a  covering  of 
hairs  or  some  other  material  may  be  present  and  lessen  loss  of 


Xerophytic  conditions.     A  typical  desert. 

moisture  by  evaporation.  The  conditions  of  extreme  dryness 
under  which  such  plants  live  is  called  xerophytic,  and  such 
plants  are  known  as  xerophytes.  Examples  of  xerophytes  are 
the  cacti,  yuccas,  agaves,  etc. 

Halophytes.  —  If  the  water  or  saturated  soil  in  which  the  plant  lives 
contains  salts,  such  as  sea  salt  or  the  alkali  salts  of  some  of  our  Western 
lakes,  then  the  conditions  are  said  to  be  halophytic,  and  a  plant  livdng 
under  such  conditions  is  known  as  8  halophyte. 

Halophytes  show  many  characteristics  which  xerophytes  show,  spines 
or  hairs,  thick  epidermis,  fleshy  leaves,  all  being  characters  which  show 
that  the  water  supply  of  the  plant  is  Umited.  The  density  of  the  salt 
water  in  the  soil  makes  it  difficult  for  the  plant  to  absorb  water ;  hence 
these  characters  are  developed. 

Mesophytes.  —  Most  plants  in  the  Temperate  Zone  occupy  a 
place  midway  between  the  xerophytes  on  one  hand  and  hydro- 
phytes on  the  other.     They  are  plants  which  require  a  moderate 

HUNT.  ES.  BIO. 11 


162    PLANTS   MODIFIED   BY   THEIR   SURROUNDINGS 

amount  of  water  in  the  soil  and  air  surrounding  them.  Such  are 
most  of  our  forest  and  fruit  trees,  and  most  of  our  garden  vege- 
tables. Conditions  of  moderate  moisture  are  called  mesophytic; 
the  plants  living  thus  are  known  as  mesophytes. 

It  may  easily  be  seen  that  plants  which  are  mesophytes  at  one 
time  may  under  some  conditions  of  weather  be  forced  to  undergo 
xerophytic  or  hydrophytic  conditions.  An  oak  tree  may  receive 
no  water  through  the  roots  during  the  winter  because  the  surface 


A  nit.'a(jpli.\Lic  ctniditiuu.     .V  \alli.'>-  in  cc^utrcU  \r\v  York. 


of  the  ground  is  frozen,  thus  preventing  w^ater  from  finding  its  way 
below  the  surface ;  on  the  other  hand,  during  excessive  rains  in 
the  spring  it  might  exist  for  a  time  under  almost  hydrophytic 
conditions.  But  many  trees  are  annually  killed  in  districts  where 
lumbering  is  going  on  through  the  damming  of  streams  and  forma- 
tion of  artificial  ponds,  which  increase  the  water  supply  of  the  trees 
near  by  and  soon  kill  them. 

Other  Factors.  —  It  is  a  matter  of  common  knowledge  that  plants 
in  different  regions  of  the  earth  differ  greatly  from  one  another  in 
shape,  size,  and  general  appearance.     If  we  study  the  causes  for 


PLANTS  MODIFIED   BY   THEIR  SURROUNDINGS    163 


these  changes,  it  becomes  evident  that  the  very  same  factor,  water 
supply,  which  governs  hydrophytic,  xerophytic,  and  mesophytic 
conditions,  determines,  at  least  in  part,  the  habits  of  the  plants 
growing  in  a  given  region  —  be  it  in  the  tropics  or  arctic  regions. 
But  in  addition  to  water  supply,  the  factors  of  temperature,  light, 
soil,  wind,  etc.,  all  play  important  parts  in  determining  the  form 
and  structure  of  a  plant. 


The  effect  of  wind  upon  txees  in  an  exposed  location.    Photograph  by  W.  C.  Barbour. 

Cold  Regions.  —  Here  plants,  which  in  lowland  regions  of  greater 
warmth  and  moisture  have  a  tall  form  and  luxuriant  foliage,  are 
stunted  and  dwarfed ;  the  leaves  are  smaller  and  tend  to  gather  in 
rosettes,  or  are  otherwise  closely  placed  for  warmth  and  protection. 
As  we  climb  a  mountain  we  find  that  the  average  size  of  plants 
decreases  as  we  approach  the  Une  of  perpetual  snow.  The  largest 
trees  occur  at  the  base  of  the  mountains ;  the  same  species  of  trees 
near  the  summit  appear  as  mere  shrubs.  Continued  cold  and  high 
winds  are  evidently  the  factors  which  most  influence  the  slow  growth 
and  the  size  and  shape  of  plants  near  the  mountain  tops.    Cold, 


164    PLANTS   MODIFIED   BY   THEIR  SURROUNDINGS 


little  light  during  the  short  days  of  the  long  winter,  and  a  slight 
amount  of  moisture  all  act  upon  the  vegetation  of  the  arctic  region, 
tending  toward  very  slow  growth  and  dwarfed  and  stunted  form. 


Polar  limit  of  trees,  northern  Russia.     All  these  trees  are  full  grown,  and  most  of 
them  are  almost  one  hundred  years  old. 

Vegetation  of  the  Tropics.  —  A  rank  and  luxuriant  growth  is 
found  in  tropical  countries  with  a  uniformly  high  temperature  and 

large  rainfall.  In 
general  it  may  be 
estimated  that  the 
rainfall  in  such 
countries  is  at 
least  twice  as 
great   as  that  of 


Region  of  Lichens. 
Region  of  Grasses. 

Shrubby  Region. 

5Z5y!MJl  WV?SM\^^'""  °'  cinchona  t 


^  /^^^^^^^%"^^^^i^UmltotOTdin&Ty\argetTeefi.    NcW    York    StatC, 


y^r:^^.!^^^^  .^     ,.,       as    great. 

-^  ■  '  <.*A>"^^^Jrv''trT^    Region  of  Palms.    ***^      &ic«,u 

,  T  i:^:r>P^yikyj:.  l^^^^  abundant 


Regions  of  the  Vine. 

\    Region  of  Tree-ferns. 


and  in  many  cases 

three  to  four  times 

An 

water 

Plant  regions  in  a  tropical  mountain.    Explain  the  diagram.  Supply,      together 


PLANTS  MODIFIED  BY   THEIR  SURROUNDINGS    165 

with  an  average  temperature  of  over  80°  Fahrenheit,  causes  ex- 
tremely rapid  growth.  One  of  the  bamboo  family,  the  growth  of 
which  was  measured  daily,  was  found  to  increase  in  length  on  the 
average  nearly  three  inches  in  the  daytime  and  over  five  inches 
during  each  night.  The  moisture  present  in  the  atmosphere 
allows  the  growth  of  many  air  plants  (epiphytes),  which  take  the 
moisture  directly  from  the  air  Iw  means  of  aerial  roots. 


Conditions   in   a   moist,    s.-niitropical   forest.     The  so-called   "Plorida  moss"  is  a 
flowering  plant.     Notice  the  resurrection  ferns  on  the  tree  trunk. 


The  absence  of  cold  weather  in  tropical  countries  allows  trees 
to  mature  without  a  thick  coating  of  bark  or  corky  material, 
plants  all  having  a  green  and  fresh  appearance.  Monocotyledo- 
nous  plants  prevail.  Ferns  of  all  varieties,  especially  the  largest 
tree  ferns,  are  abundant. 

Plant  Life  in  the  Temperate  Zones.  —  In  the  state  of  New  York, 
conditions  are  those  of  a  typical  temperate  flora.  Extremes  of 
cold  and  heat  are  found,  the  temperature  ranging  from  30°  Fahren- 
heit below  zero  in  the  winter  to  100°  or  over  in  the  summer.  Condi- 
tions of  moisture  show  an  average  rainfall  of  from  24  inches  to  52 


166    PLANTS  MODIFIED   BY   THEIR  SURROUNDINGS 


inches.      Conditions  of  moisture  in  the  country  cause  great  differ- 
ences in  the  plant  covering. 

In  the  eastern  part  of  the  United  States  the  rainfall  is  sufficient 
to  give  foothold  to  great  forests,  which  aid  in  keeping  the  water  in 
the  soil.  In  the  Middle  West  the  rainfall  is  less,  the  prairies  are 
covered  with  grasses  and  other  plants  which  have  become  adapted 
to  withstand  dryness.  In  the  desert  region  of  the  Southwest  we 
find  true  xerophytes,  cacti,  switch  plants,  yuccas,  and  others,  all 


A  rock  society.     Photograph  by  W.  C.  Barbour. 

plants  which  are  adapted  to  withstand  almost  total  absence  of 
moisture  for  long  periods.  In  the  Temperate  Zone  the  water  supply 
is  the  primary  factor  which  determines  the  form  of  plant  growth. 
Plant  Formations  and  Societies.^  —  All  of  the  factors  alluded  to 
act  upon  the  plants  we  find  living  together  in  a  forest,  a  sunny 

1  Plant  Societies.  Field  Work.  —  Any  boy  or  girl  who  has  access  to  a  vacant  lot 
or  city  park  can  easily  see  that  plants  group  themselves  into  societies.  Certain 
plants  live  together  because  they  are  adapted  to  meet  certain  conditions.  Societies 
of  plants  exist  along  the  dusty  edge  of  the  roadside,  under  the  trees  of  the  forest, 
along  the  edge  of  the  brook,  in  a  swamp  or  a  pond.  It  should  be  the  aim  of  the 
field  trips  to  learn  the  names  of  plants  which  thus  associate  themselves  and  the  condi- 
tions under  which  they  live,  and  especially  their  adaptations  to  the  given  conditions. 
Suggestions  for  such  excursions  are  found  in  Andrews,  Botany  All  the  Year  Round; 
Lloyd  and  Bigelow,  The  Teaching  of  Biology ;  and  Ganong,  The  Teaching  Botanist. 
A  convenient  form  for  an  excursion  is  found  in  Hunter  and  Valentine,  Manual,  page 
202.     This  trip  may  be  taken  in  the  early  fall. 


PLANTS   MODIFIED   BY   THEIR  SURROUNDINGS    167 

meadow,  along  a  roadside,  or  at  the  edge  of  a  pond.  Any  one 
familiar  with  the  country  knows  instinctively  that  we  find  certain 
plants,  and  those  plants  only,  living  together  under  certain  condi- 
tions. For  example,  the  wild  columbine,  certain  ferns,  and  mosses, 
and  other  shade,  moisture,  and  rock-loving  plants  are  found  to- 
gether on  rocky,  shaded  hillsides.  We  should  not  think  of  looking 
for  daisies  and  buttercups  there  any  more  than  we  should  look  for 


v.^-  # 


'3I^- 


Plant  societies  near  a  pond.     Notice  that  the  plant  groups  are  arranged  in  zones 
with  reference  to  the  water  supply,  the  true  mesophytes  being  in  the  background. 

the  marsh  marigold  (Caltha  paliistris)  or  the  pickerel  weed  {Ponte- 
deria  cor  data)  in  a  dry  and  sunny  field. 

Plants  associated  under  similar  conditions,  as  those  of  a  forest, 
meadow,  or  swamp,  are  said  to  make  up  a  formation,  and  a  plant 
formation  is  brought  about  by  the  conditions  of  its  immediate 
surroundings,  the  habitat  of  its  members.  If  we  investigate  a  plant 
formation,  we  find  it  to  be  made  up  of  certain  dominant  species  of 
plants ;  that  here  and  there  definite  communities  exist,  made  up 
of  groups  of  the  same  kind  of  plants.  We  can  see  that  every  one  of 
these  plant  groups  in  the  society  evidently  originally  came  from 
single  individuals  of  species  which  thrive  under  the  peculiar  condi- 
tions of  soil,  water,  light,  etc.,  that  we  find  in  this  spot.     These 


168    PLANTS  MODIFIED  BY  THEIR  SURROUNDINGS 


single  plants  have  evidently  given  rise  to  the  members  of  each  Httle 
family  group,  and  thus  have  populated  the  locality. 

So  we  find  among  plants  communal  conditions  similar  to  those 
among  some  animals.  The  many  individuals  of  the  community 
live  under  similar  conditions;  they  need  the  same  substances  from 
the  air,  the  water,  the  soil.  They  all  need  the  light;  they  use  the 
same  food.  Therefore  there  must  be  competition  among  them, 
especially  between  those  near  to  each  other.  The  plants  which  are 
strongest  and  best  fitted  to  get  what  they  need  from  their  surround- 
ings live;  the  weaker  ones  are  crowded  out  and  die. 

But  their  lives  are  not  all  competition.  The  dead  plants  and 
animals  give  nitrogenous  material  to  the  living  ones,  from  which  the 

latter  make  living  matter ; 
some  bacteria  provide  cer- 
tain of  the  green  plants 
with  nitrogen ;  many  of  the 
green  plants  make  food 
for  other  plants  lacking 
chlorophyll,  while  some 
algse  and  fungi  actually 
live  together  in  such  a 
way  as  to  be  of  mutual 
benefit  to  each  other.  The 
larger  plants  may  shelter 
the  smaller  ones,  protect- 
ing them  from  wind  and 
storm,  while  the  trees  hold  the  moisture  in  the  ground,  giving  it 
off  slowly  to  other  plants.  Animals  scatter  and  plant  the  seeds 
far  and  wide,  and  man  may  even  plant  entire  colonies  in  new 
localities. 

How  Plants  invade  New  Areas.  —  New  areas  are  tenanted  by 
plants  in  a  similar  manner.  After  the  burning  over  of  a  forest,  we 
find  a  new  generation  of  plants  springing  up,  often  quite  unlike  the 
former  occupants  of  the  soil.  First  come  the  fireweed  and  other 
light-loving  weeds,  planted  by  means  of  their  wind-blown  seeds. 
With  these  are  found  patches  of  berries,  the  seeds  of  which  were 
brought  by  birds  or  other  animals.  A  little  later,  quick-growing 
trees  having  seeds  easily  carried  for  some  distance  by  the  Tvnnd, 


A    community    of    trilliums.      Photograph    by 
W.  C.  Barbour. 


PLANTS   MODIFIED  BY   THEIR  SURROUNDINGS    169 

like  the  aspen  and  wild  cherry,  which  have  the  birds  to  help  them 
out,  invade  the  territory.  Eventually  we  may  have  the  area  re- 
tenanted  by  its  former  inhabitants,  especially  if  the  destruction  of 
the  original  forest  was  not  complete. 

In  like  manner,  on  the  upper  mountain  meadow  or  by  the  sand 
dunes  of  the  seashore,  wherever  plants  place  their  outposts,  the 


A  plant  outpost.     Tiu'  struKult-  li< n'  is  keen.    Tlie  advaiicing  sand  has 
killed  the  trees  in  the  foreground. 

advance  is  made  from  some  thickly  inhabited  area,  and  this  advance 
is  always  aided  or  hindered  by  agencies  outside  of  the  plant  —  the 
wind,  the  soil,  water,  or  by  animals.  Thus  the  seeds  obtain  a  foot- 
hold in  new  territory,  and  thus  new  lands  are  captured,  held,  and 
lost  again  by  the  plant  comnmnities. 


Reference  Books 

elementary 

Sharpc,  A  Laboratory  Manual  for  the  Solution  of  Problems  in  Biology. 

Book  Company. 
Andrews,  Botany  All  the  Year  Round.     American  Book  Company. 
Bergen  and  Davis,  Principles  of  Botany.     Ginn  and  Company. 
Coulter,  Plant  Relations.     D.  Appleton  and  Company. 
Leavitt,  Outlines  of  Botany.     American  Book  Company. 
Stevens,  Introduction  to  Botany.     D.  C.  Heath  and  Company. 


American 


ADVANCED 

Clements,  Plant  Physiology  and  Ecology.    Henry  Holt  and  Company. 
Coulter,  Barnes,  and  Cowles,  A  Textbook  of  Botany,  Vol.  II.     American  Book  Com- 
pany. 
Kerner,  Natural  History  of  Plants.    4  vols.     Henry  Holt  and  Company. 
Schimper,  Plant  Geography.    Clarendon  Press, 


XIII.  HOW  PLANTS  BENEFIT  AND  HARM  MANKIND 

Problem  XXII,    Tlie  relations  of  fungi  to  man.    {Laboratory 
Manual,  Proh.  XXIL) 
(a)  Yeast, 
(h)  Other  fungi. 

The  Economic  Value  of  Plants.  —  Besides  the  other  relations 
existing  between  plants  and  animals,  there  is  a  relation  between 
man  and  plants  measurable  in  dollars  and  cents.  Plants  are  of 
direct  value  or  harm  to  man.  We  call  this  an  economic  relation. 
We  have  seen  how  they  supply  him  with  his  cereals  and  flour, 
his  fruits  and  garden  vegetables,  his  nuts  and  spices,  his  beverages 
and  the  sugar  to  sweeten  them,  his  medicines  and  his  dyestuffs. 
They  supply  the  material  out  of  which  many  of  his  clothes  are 
made,  the  thread  with  which  they  are  sewed  together,  the  paper  which 
covers  the  package  in  which  they  are  delivered,  and  the  string  with 
which  the  package  is  tied.  The  various  uses  of  the  forest  have  been 
mentioned  before;  the  need  of  trees  to  protect  the  earth,  their 
usefulness  in  the  holding  of  the  water  supply,  their  direct  economic- 
importance  for  lumber  and  firewood.  Many  of  us  forget,  too,  that 
much  of  the  energy  released  on  this  earth  to  man  as  heat,  light,  or 
motive  power  comes  from  the  dead  and  compressed  bodies  of  plants 
which  thousands  of  years  ago  lived  on  the  earth  and  now  form  coal. 
Plants  are  thus  seen  to  be  of  immense  direct  economic  importance 
to  mankind. 

The  Harm  Plants  Do.  —  Unfortunately,  plants  do  not  all  benefit 
mankind.  We  have  seen  the  harm  done  by  weeds,  which  scatter 
their  numerous  seeds  far  and  wide  or  by  other  devices  gain  a  foot- 
hold and  preempt  the  territory  which  useful  plants  might  occupy 
were  they  able  to  cope  with  their  better-equipped  adversaries. 
Plants  with  poisonous  seeds  and  fruits  are  undoubtedly  responsi- 
ble for  the  death  of  many  animals. 

But  by  far  the  most  harmful  plants  to  mankind  are  the  fungi. 

170  • 


HOW  PLANTS  BENEFIT  AND   HARM   MANKIND     171 

Hundreds  of  millions'  yearly  damage  may  l)o  laid  directly  to  them. 
More  than  that,  they  are  doubtless  responsible  for  one  half  of  the 
total  human  deaths.     This  is  because  of  their  parasitic  habits. 

Yeast.  —  Although  as  a  group  the  fungi  are  harmful  to  man  in  the 
economic  sense,  nevertheless  there  are  some  fungi  that  stand  in  a  decidedly 
helpful  relationship  to  the  human  race.  Chief 
of  these  are  the  yeast  plants.  Yeasts  are 
found  to  exist  in  a  wild  state  in  very  many 
parts  of  the  world.  They  are  found  on  the 
skins  of  fruits,  in  the  soil  of  vineyards  and 
orchards,  in  cider,  beer,  and  other  fluids, 
while  they  may  exist  in  a  dry  state  almost 
anywhere  in  the  air  around  us.  In  a  culti- 
vated state  we  find  them  doing  oiu*  work  as  A,  yeast  plant  bud  just  form- 
the  agents  which  cause  the  rising  of  bread,  ing ;  B,  bud  almost  ready 
and  the  fermentation  in  beer  and  other  alco-  to  l^^ve  parent  cell.  Note 
holic  fluids.  **^^   ""^^^"«    (^    dividing 

Size  and  Shape,  Manner  of  Growth,  etc.-  ^"'^J^^J^'f'  (^fterSedg- 
_-  ^  1  .       1  *   •  wick  and  Wilson.) 

The  common  compressed  yeast  cake  contains 

millions  of  these  tiny  plants.  In  its  simplest  form  a  yeast  plant  is  a 
single  cell.  If  you  shake  up  a  bit  of  a  compressed  yeast  cake  in  a  mixture 
of  sugar  and  water  and  then  examine  a  drop  of  the  milky  fluid  after  it  has 
stood  overnight,  it  will  be  seen  to  contain  vast  numbers  of  yeast  plants. 
The  shape  of  such  a  plant  is  ovoid,  each  cell  showing  under  the  micro- 
scope the  granular  appearance  of  the  protoplasm  of  which  it  is  formed. 
Look  for  tiny  clear  areas  in  the  cells ;  these  are  vacuoles,  or  spaces  filled 
with  fluid.  The  nucleus  is  hard  to  find  in  an  unstained  yeast  cell;  it 
can,  however,  be  found  in  specimens  which  liave  been  prepared  by  stain- 
ing the  previously  killed  cells  with  iron-hsematoxylin.*  Yeast  cells  repro- 
duce very  rapidlj^  by  a  process  of  budding,  a  part  o^  the  parent  cell 
forming  one  or  more  smaller  daughter  cells  which  eventually  become  free 
from  the  parent. 

Most  yeast  plants  seem  to  produce  spores  at  some  time  during  their 
existence.  The  spores  are  formed  within  a  yeast  cell,  as  many  as  four 
being  produced  within  a  single  cell.  These  spores,  under  proper  condi- 
tions, will  germinate  and  give  rise  to  new  plants. 

Conditions  favorable  to  Growth  of  Yeast.  —  Under  certain  conditions 
yeast,  when  added  to  dough,  will  cause  it  to  rise.  We  also  know  that  yeast 
has  something  to  do  with  the  process  we  call  fermentation.  The  following 
home  experiment  will  throw  some  light  on  these  points :  — 

Label  three  pint  fruit  jars  A,  B,  and  C.  Add  one  fourth  of  a  com- 
pressed yeast  cake  to  two  cups  of  water  containing  two  tablespoonfuls  of 
molasses  or  sugar.     Stir  the  mixture  well  and  divide  it  into  three  equal 

>  See  Lee,  Vade  Mecum,  or  Sedgwick  and  Wilson,  General  Biology. 


172    HOW  PLANTS  BENEFIT  AND   HARM  MANKIND 

parts  and  pour  them  into  the  jars.  Place  covers  on  the  jars.  Put  jar  A 
in  the  ice  box  on  the  ice,  and  jar  B  over  the  kitchen  stove  or  near  a  radiator  ; 
boil  the  jar  C  by  immersing  it  in  a  dish  of  boiling  water,  and  place  it  next 
to  B.  After  forty-eight  hours,  look  to  see  if  any  bubbles  have  made 
their  appearance  in  any  of  the  jars.  If  the  experiment  has  been  successful 
only  jar  B  will  show  bubbles.  After  bubbles  have  begun  to  appear  at  the 
surface,  the  fluid  in  jar  B  will  be  found  to  have  a  sour  taste  and  will  smell 
unpleasantly.  The  gas  which  rises  to  the  surface,  if  collected  and  tested, 
will  be  found  to  be  carbon  dioxide.  The  contents  of  jar  B  are  said  to  have 
fermented.  Evidently,  the  growth  of  yeast  will  take  place  only  under 
conditions  of  moderate  warmth  and  moisture. 

Fermentation  a  Chemical  Process.  —  In  this  process  of  growth  the 
sugar  of  the  solution  in  which  they  live  is  broken  up  by  a  digestive  fer- 
ment or  enzyme  into  carbon  dioxide  and  alcohol.  This  may  be  expressed 
by  the  following  chemical  formula:  CeHisOe  =  2(C2H60)  +  2(C02). 
This  means  that  the  sugar  forms  alcohol  and  carbon  dioxide.  This  pro- 
cess, which  we  call  fermentation,  is  of  the  greatest  importance  in  the 
brewing  industry. 

Beer-Making.  —  Brewers'  yeasts  are  cultivated  with  the  greatest  care ; 
for  the  different  flavors  of  beer  seem  to  depend  largely  upon  the  condi- 
tion of  the  yeast  plants.  Beer  is  made  in  the  following  manner  :  Sprouted 
barley,  called  malt,  in  which  the  starch  of  the  grain  has  been  changed  to 
grape  sugar  by  digestion,  is  killed  by  drying  in  a  hot  kiln.  The  malt  is 
dissolved  in  water,  and  hops  are  added  to  give  the  mixture  a  bitter  taste. 
Now  comes  the  addition  of  the  yeast  plants,  which  multiply  rapidly  under 
the  favorable  conditions  of  food  and  heat.  Fermentation  results  on  a 
large  scale  from  the  breaking  down  of  the  grape  sugar,  the  alcohol  re- 
maining in  the  fluid,  and  the  carbon  dioxide  passing  off  into  the  air.  The 
process  is  stopped  at  the  right  instant,  and  the  beer  is  stored  either  in  bottles 
or  casks. 

Bread-Making.  —  In  bread-making  the  rapid  growth  of  the  yeast 
plants  is  facilitated  by  placing  the  pan  containing  the  mixture  in  a  warm 
place  overnight.  Fermentation  results  from  the  digestion  of  grape  sugar 
by  the  yeasts,  this  grape  sugar  being  part  of  the  starch  in  the  flour  which 
is  changed  by  the  diastase  present  in  the  grain  of  wheat.  The  carbon 
dioxide  remains  in  the  dough  as  the  bubbles  so  familiar  to  the  bread- 
maker,  the  alcohol  produced  being  evaporated  during  the  process  of  baking. 

Yeast  Saprophytes.  —  The  above  paragraphs  show  yeast  plants  to  be 
saprophytes.  In  order  to  grow,  they  must  be  supplied  with  food  materials 
that  will  build  up  protoplasm  as  well  as  release  energy.  This  food  they 
obtain  from  the  organic  matter  in  the  fluids  in  which  they  happen  to  be. 

The  Shelf  Fungus ;  a  Saprophyte.  —  A  near  relation  to  the  mush- 
room is  the  bracket  or  shelf  fungus.  This  fungus  is  familiar  to  any 
one  who  has  been  in  a  forest  in  this  part  of  the  country. 


HOW  PLANTS  BENEFIT  AND  HARM  MANKIND    173 


An  examination  of  specimens  shows  that  the  shelf  or  bracket  is 
in  reaUty  a  spore  case,  which  is  usually  provided  with  a  very  con- 
siderable number  of  holes,  slits,  or  pores  in  which  the  spores  are 
formed.  The  spores  when  ripe  escape  from  the  under  surface  of 
the  spore-bearing  body  through  the  minute  pores.  The  mycelium 
is  within  the  tissue  of  the 
tree.  Remove  the  bark  from 
any  tree  infected  with  bracket 
fungus,  and  you  will  find  the 
silvery  threads  of  the  myce- 
lium sending  their  greedy 
hyphue  to  all  parts  of  the 
wood  adjacent  to  the  spot 
first  attacked  by  the  fungus. 
This  fungus  begins  its  life  by 
the  lodgment  of  a  spore  in 
some  part  of  the  tree  which 
has  become  diseased  or  broken. 
Once  established  on  its  host, 
it  spreads  rapidly.  There  is 
no  remedy  except  to  kill  the 
tree  and  burn  it,  so  as  to 
destroy  the  spores.  Many 
fine  trees,  sound  except  for  a 
slight  bruise  or  other  injury,  are  annually  infected  and  eventually 
killed.  In  cities  thousands  of  trees  become  infected  through 
careless  hitching  of  horses  so  that  the  horse  may  gnaw  or  crib  on  the 
tree,  thus  exposing  a  fresh  surface  on  which  spores  may  obtain  lodg- 
ment and  grow  (see  page  142). 


Shelf  or  bracket  fungi  on  dead  tree  trunk. 


Suggestions  for  Field  Work.  —  A  field  trip  to  a  park  or  grove  near 
home  may  show  the  great  destruction  of  timber  by  this  means.  Count  the 
number  of  perfect  trees  in  a  given  area.  Compare  it  with  the  number  of 
trees  attacked  by  the  fungus.  Does  the  fungus  appear  to  be  transmitted 
from  one  tree  to  another  near  at  hand  ?  In  how  many  instances  can  you 
discover  the  point  where  the  fungus  first  attacked  the  tree? 


Parasitic  Fungi.  —  Of  even  more  importance  are  the  fungi  that 
attack  a  living  host,  true  parasites.     The  most  important  of  such 


174    HOW  PLANTS   BENEFIT  AND   HARM   MANKIND 


plants  from  an  economic  standpoint  are  the  rusts,  smuts,  and  mil- 
dews which  prey  upon  grain,  corn,  and  other  cultivated  plants. 
Some  fungi  are  also  parasitic  upon  fruit  and  shade  trees.      The 

chestnut  canker,  a  fungus 
recently  introduced  on 
chestnuts  planted  near 
New  York  city,  has  within 
five  years  practically  de- 
stroyed all  the  chestnut 
trees  within  a  radius  of 
twenty  miles  of  the  city, 
and  is  estimated  to  have 
done  $10,000,000  damage 
already.  Damage  extending  to  hundreds  of  millions  of  dollars  is 
annually  done  by  the  fungi. 


Corn  smut,  a  fungus  parasitic  on  corn  ;  the  black 
mass  consists  almost  entirely  of  ripe  spores. 


Wheat  Rust.  —  Wheat  rust  is  probably  the  most  destructive  parasitic 
fungus.  For  hundreds  of  years  wheat  rust  has  been  the  most  dreaded 
of  plant  diseases,  because  it  destroys  the  one  harvest  upon  which  the 
civilized  world  is  most  dependent.  For  a  long  time  past  the  appear- 
ance of  rust  has  been  associated  with  the  presence  of  barberry  bushes  in 
the  neighborhood  of  the  wheat  fields.  Although  laws  were  enacted  nearly 
two  hundred  years  ago  in  New  England  to  provide  for  the  destruction  of 
barberry  bushes  near  infected  wheat  fields,  nothing  was  actually  known 
of  the  relation  existing  between  the  rust  and  the  barberry  until  recently. 
It  has  now  been  proved  beyond  doubt  that  the  wheat  rust  passes  part  of 
its  life  as  a  parasite  on  the  barberry  and  from  it  gets  to  the  wheat  plant, 
where  it  undergoes  a  complicated  life  history.  The  wheat  leaf,  its  nour- 
ishment and  living  matter  used  as  food  by  the  parasite,  soon  dies,  and  no 
grain  is  produced.  Some  wheat  rusts  do  not  have  two  hosts,  living  only 
on  the  wheat  and  wintering  over  by  means  of  thick-walled  spores  which 
remain  in  the  stubble  or  in  the  ground  until  the  young  wheat  plants 
appear  the  following  year. 

Mildews.  —  Another  group  of  fungi  that  are  of  considerable  economic 
importance  is  made  up  of  the  sac  fungi.  Such  fungi  are  commonly  called 
mildews.  Some  of  the  most  easily  obtained  specimens  come  from  the  Ulac, 
rose,  or  willow.  These  fungi  do  not  penetrate  the  host  plant  to  any  depth, 
but  cover  the  leaves  of  the  host  with  the  whitish  threads  of  the  mycelium. 
Hence  they  may  be  killed  by  means  of  applications  of  some  fungus-kill- 
ing fluid,  as  Bordeaux  mixture.^     They  obtain  their  food  from  the  outer 

1  See  Goff  and  Mayne,  First  Principles  of  Agriculture,  page  59,  for  formula  of 
Bordeaux  mixture. 


HOW  PLANTS  BENEFIT  AND   HARM   MANKIND    175 

layer  of  cells  in  the  leaf  of  the  host.  Among  the  useful  plants  preyed 
upon  by  this  group  of  fungi  are  the  plum,  cherry,  and  peach  trees.  (The 
diseases  known  as  ])lack  knot  and  peach  curl  are  thus  caused.)  Other 
sac  fungi  are  the  morels  and  truffles,  the  downy  mildews,  blue  and  green 
molds,  and  many  other  forms.  One  important  member  of  this  group  is 
the  tiny  parasite  found  on  rye  and  other  grains,  which  gives  us  the  drug 
ergot. 

Problem  XXTII.    A  study  of  bacteria  and  of  some  of  their 
relations  to  man.    (Laboratory  Manual,  Frob.  XXIIIJ 
(a)  Conditions  of  gi'owth. 
(jb)  Some  relations  to  man. 
(c)  Som,e  methods  of  fighting  Jiarmful  bacterid. 


Bacteria,  —  The  bacteria  are  found  in  the  earth,  the  water, 
and  the  air.  "  Anywhere  but  not  everywhere,"  as  one  writer 
has  put  it.  They  swarm  in  stale  milk,  in  impure  water,  in  the  liv- 
ing bodies  of  plants  and  animals,  and  in 
any  decaying  material.  These  tiny  plants, 
"  man's  invisible  friends  and  foes,"  are  of 
such  importance  to  mankind  that  thou- 
sands of  scientists  devote  their  whole  lives 
to  their  study,  and  a  science  called  bac- 
teriology has  been  named  after  them. 

Size  and  Form.  —  In  size,  bacteria  are 
the  most  minute  plants  known.  A  bac- 
terium of  average  size  is  about  inrVg-  of  an 
inch  in  length,  and  perhaps  25000  of  an 
inch  in  diameter.  Some  species  are  much 
larger,  others  smaller.  A  common  spheri- 
cal form  is  3~5  on  of  an  inch  in  diameter.  It 
will  mean  more  to  us,  perhaps,  if  we  re- 
member that  several  millions  of  bacteria  of 
average  size  msLj  be  placed  within  the  area 
formed  in  this  letter  0.  Three  well-defined 
forms  of  bacteria  are  recognized :  a  spheri- 
cal form  called  a  coccus,  a  rod-shaped 
bacterium,  the  bacillus,  and  a  spiral  form,  the  spirillum.  Some 
bacteria  are  capable  of  movement  when  living  in  a  fluid.     Such 


Bacteria,  highly  magnified  : 

a,  the  germ  of  typhoid 
fever,  stained  to  show  the 
cilia,  little  threads  of  liv- 
ing matter  by  means  of 
which  locomotion  is  ac- 
complished ;  b,  a  spiral 
ciliated  form ;  c,  a  rod- 
shaped  form,  in  chains ; 
d,  a  spherical  form.  —  a, 

b,  from  Engler  and  Prantl. 


176    HOW  PLANTS  BENEFIT  AND  HARM  MANKIND 


movement  seems  to  be  caused  by  tiny  lashlike  threads  of  proto- 
plasm called  cilia.  The  cilia  project  from  the  body,  and  by  a  rapid 
movement  cause  locomotion  to  take  place.  Bacteria  reproduce 
with  almost  incredible  rapidity.  It  is  estimated  that  a  single 
bacterium,  by  a  process  of  division  called  fission,  will  give  rise  to 
over  16,700,000  others  in  twenty-four  hours.  Dr.  Prudden  has 
estimated  that  such  a  bacterium,  if  allowed  to  develop  unchecked 
for  five  days,  would  fill  all  the  oceans  of  this  earth  to  a  depth  of  one 
mile.  Under  unfavorable  conditions  they  stop  dividing  and  form 
spores,  in  which  state  they  remain  until  conditions  of  temperature 
and  moisture  are  such  that  growth  may  begin  again. 

Method  of  Study.  —  In  order  to  get  a  number  of  bacteria  of  a 
given  kind  to  study,  it  becomes  necessary  to  grow  them  in  what  is 

known  as  a  pure  culture.  This 
is  done  by  first  growing  the 
bacteria  in  some  medium  such 
as  beef  broth,  gelatin,  or  on 
potato.^  The  material  used  as 
a  growth  medium  is  at  first 
sterilized  by  heating  to  such  a 
temperature  as  to  kill  all  life 
that  might  be  there.  If  the 
material  is  exposed  to  the  air 
of  the  schoolroom  in  a  shallow 
dish  (known  as  a  Petri  dish),  or 
in  a  test  tube  in  the  case  of 
beef  broth,  for  say  five  minutes, 
and  if  then  the  dish  or  tube  is 
covered  and  put  away  in  a 
warm  place  for  a  day  or  two,  little  spots  will  appear  on  the  surface 
of  the  gelatin  or  potato,  or  the  beef  broth  will  become  cloudy. 

Pure  Culture.  —  The  spots  are  colonies  composed  of  millions  of 
bacteria.  If  now  we  wish  to  study  one  given  form,  it  becomes  nec- 
essary to  isolate  them  from  the  others  on  the  plate.  This  is  done  by 
the  following  process :  A  platinum  needle  is  first  passed  through  a 
flame  to  sterilize  it;  that  is,  to  kill  all  living  things  that  maybe  on  the 

1  For  directions  for  making  a  culture  medium,  see  Peabody,  Manual  of  Physiology. 
Culture  tubes  may  be  obtained,  already  prepared,  from  Parke,  Davis,  and  Company. 


A  Petri  dish  culture  of  bacteria ;  the  colo- 
.  uies  of  bacteria  are  the  little  spots  of 
various  size  and  color. 


HOW   PLANTS   BENEFIT  AND   HARM   MANKIND    177 

needle  point.  Then  the  needle,  which  cools  very  quickly,  is  dipped 
in  a  colony  containing  the  bacteria  we  wish  to  study.  This  mass  of 
bacteria  is  quickly  transferred  to  another  sterilized  plate,  and  this 
plate  is  immediately  covered  to  prevent  any  other  forms  of  bacteria 
from  entering.  When  we  have  succeeded  in  isolating  a  certain 
kind  of  l)acteria  in  a  given  dish,  we  are  said  to  have  a  pure  culture. 

Bacteria  cause  Decay.  * —  Bacteria  in  several  ways,  either  directly 
or  indirectly,  affect  mankind.  First  of  all,  they  cause  decay.  All 
organic  matter,  in  whatever  form,  is  sooner  or  later  decomposed  by 
the  action  of  untold  millions  of  bacteria  which  live  in  the  air,  water, 
and  soil.  To  a  considerable  degree,  then,  these  bacteria  are  useful 
in  feeding  upon  the  dead  bodies  of  plants  or  animals,  which  other- 
wise would  soon  cover  the  surface  of  the  earth  to  the  exclusion  of 
everything  else.  Bacteria  may  thus  be  scavengers.  They  oxidize 
organic  materials,  changing  them  to  compounds  of  nitrogen  that 
can  be  absorbed  by  plants  and  used  in  building  protoplasm. 
Without  bacteria  and  fungi  it  would  be  impossible  for  life  to  exist 
on  the  earth,  for  green  plants  would  Ix?  unaV)lc  to  get  the  raw  food 
materials  in  forms  that  could  l>e  used  in  making  food  and  living  mat- 
ter.    In  this  respect  they  are  of  the  greatest  service  to  mankind. 

When  bacteria  grow  in  sufficient  numbers  upon  foods,  meat, 
fish,  or  vegetables,  they  spoil  them,  and  may  form  poisonous  sub- 
stances called  ptomaines.  Such  substances  are  formed  as  waste 
products  by  the  bacteria,  and  are  given  off  into  the  material  in 
which  the  bacteria  are  living.  Thus  we,  upon  eating  the  food  con- 
taining these  poisons,  may  become  violently  ill  as  the  result  of 
ptomaine  poisoning.  Fish  and  meats  that  have  been  kept  for 
some  time  in  cold  storage  are  very  easily  spoiled,  and  should  be 
avoided.  Jars  of  canned  goods  that  have  "  worked,"  that  is  in 
which  bacteria  or  yeasts  have  caused  fermentation,  are  often  unfit 
for  food. 

Relation  to  Fermentation.  —  They  may  incidentally,  as  a  result 
of  this  process  of  decay,  aid  in  the  process  of  fermentation.  In 
making  vinegar  the  yeasts  first  make  alcohol  (see  p.  172),  which 
the  bacteria  change  to  acetic  acid.  The  lactic  acid  bacteria 
which  sour  milk,  changing  the  milk  sugar  to  an  acid,  grow  very 
rapidly  in  a  warm  temperature;  hence  milk  which  is  kept  cool  or 
which  is  pasteurized  (that  is,  kept  at  a  temperature  of  about  176° 

HUNT.   ES.   BIO. 12 


178    HOW  PLANTS  BENEFIT  AND  HARM  MANKIND 


Fahrenheit  for  five  to  twenty  minutes  for  the  purpose  of  killing 
the  bacteria)  will  not  sour  readily,  if  kept  in  a  cool  place.     Why  ? 

These  same  lactic  acid  bac- 
teria may  be  useful  when 
they  sour  the  milk  for  the 
cheese-maker.  Certain 
other  bacteria  give  flavor 
to  cheese  and  butter,  while 
still  others  are  used  by  the 
tanner. 

Nitrogen-fixing  Bacteria. 
—  Still  other  bacteria,  as 
we  have  seen  before, ' '  change 
over  "  nitrogen  in   organic 


A  pasteurizing  apparatus. 


material  in  the  soil  and  even  the  free  nitrogen  of  the  air  so  that  it 
can  be  used  by  plants  in  the  form  of  a  compound  of  nitrogen.  The 
bacteria  living  in  tubercles 
on  the  roots  of  clover,  beans, 
peas,  etc.,  have  the  power 
of  thus  "  fixing  "  the  free 
nitrogen  in  the  air  found 
between  particles  of  soil. 
This  fact  is  made  use  of 
by  farmers  who  rotate  their 
crops,  growing  first  a  crop 
of  clover  or  alfalfa,  which 
produce  the  bacteria,  then 
plowing  these  up  and  plant- 
ing another  crop,  as  wheat 
or  corn,  on  the  same  area. 
The  latter  plants,  making 
use  of  the  nitrogen  com- 
pounds there,  produce  a 
larger  crop  than  when  grown 
in  ground  containing  less 
nitrogenous  material. 

Bacteria    cause     Disease.    Modules  contain  the  nitrogen  fixing  bacteria  on 

—  The  most  harmful  bac-  the  roots  of  clover. 


HOW   PLANTS   BENEFIT  AND  HARM   MANKIND    179 


teria  are  those  which  cause  disease.  This  they  do  by  becoming 
parasites  in  the  human  })ody.  Millions  upon  millions  of  bacteria 
exist  in  the  human  body  at  all  times  —  in  the  mouth,  on  the  teeth, 
and  especially  in  the  lower  part  of  the  food  tube.  Some  in  the  food 
tube  are  believed  to  be  useful,  others  harmless;  still  others  cause 
decay  of  the  teeth,  while  a  few  kinds,  if  present  there,  may  cause 
disease. 

It  is  known  that  bacteria,  like  any  other  living  things,  feed  and 
give  off  organic  waste.  This  waste,  called  a  toxin,  is  poison  to  the 
hosts  on  which  the  bacteria  live,  and  it  is  usually  the  production  of 
this  toxin  that  causes  the  symptoms  of  disease.  Some  forms, 
however,  break  down  tissues  and  plug  up  the  small  blood  vessels, 
thus  causing  disease. 

Diseases  caused  by  Bacteria.  —  It  is  estimated  that  bacteria 
cause  annually  over  50  per  cent  of  the  deaths  of  the  human  race. 
As  we  will  later  see,  a 
very  large  proportion  of 
these  diseases  might  be 
prevented  if  people  were 
educated  sufficiently  to 
take  the  proper  precau- 
tions to  prevent  their 
spread.  These  precau- 
tions might  save  the  lives 
of  some  3,000,000  of  peo- 
ple yearly  in  Europe  and 
America.  Tuberculosis, 
typhoid  fever,  diphtheria, 
pneumonia,  blood  poison- 
ing, syphilis,  and  a  score 
of  other  germ  diseases 
ought  not  to  exist.  A 
good  deal  more  than  half 
of  the  present  misery  of 
this  world  might  be  prevented  and  this  earth  made  cleaner  and  better 
by  the  cooperation  of  the  young  people  now  growing  up  to  be  our 
future  home-makers. 

Germs  or  contagious  diseases  either  enter  the    body  by  way 


A  single  cell  scrap>ed  from  the  roof  of  the  mouth  and 
highly  magnified.  The  little  dots  are  living  bac- 
teria, most  of  them  comparatively  harmless. 


180    HOW  PLANTS  BENEFIT  AND   HARM   MANKIND 


of  the  mouth  or  nose,  from  air,  food,  or  water,  or  may  be  trans- 
mitted from  some  person  having  disease  to  a  well  person  by  con- 
tact. Usually  the  germs  enter  the  body  through  some  opening, 
as  the  mouth,  or  through  a  cut  or  sore.  With  care  by  the  civic 
authorities  and  by  individuals  a  healthy  person  should  easily  keep 
from  such  diseases,  if  he  takes  proper  precautions. 

Tuberculosis.  —  The  one  disease  responsible  for  the   greatest 
number  of  deaths — perhaps  one  seventh  of  the  total  on  the  globe  — 

is  tuberculosis.  But  this  dis- 
ease is  slowly  but  surely  being 
overcome.  It  is  believed  that 
within  perhaps  fifty  3^ears,  with 
the  aid  of  good  laws  and  sani- 
tary living,  it  will  be  almost 
extinct. 

Tuberculosis  is  caused  by 
the  growth  of  a  bacterium, 
called  the  tubercle  bacillus, 
within  the  lungs  or  other  tis- 
sues of  the  human  body.  Here 
it  forms  little  tul^ers  full  of 
germs,  which  close  up  the  deh- 
cate  air  passages  in  the  lungs, 
and  in  other  tissues  give  rise  to 
hip-joint  disease,  scrofula,  lupus, 
and  other  diseases,  depending 
on  the  part  of  the  body  they  attack.  Tuberculosis  may  be  con- 
tracted by  taking  the  bacteria  into  the  throat  or  lungs  by  eating 
meat  or  drinking  milk  from  tubercular  cattle.  Especially  is  it  com- 
municated from  a  consumptive  to  a  well  person  by  kissing,  drink- 
ing, or  eating  from  the  same  cup  or  plate,  using  the  same  towels, 
or  in  any  way  coming  in  direct  contact  with  the  person  having  the 
germs  in  his  body.  Although  there  are  always  some  of  the  germs  in 
the  air  of  an  ordinary  city  street,  and  though  we  may  take  some 
of  these  germs  into  our  bodies  at  anytime,  yet  the  bacteria  seem  able 
to  gain  a  foothold  only  under  certain  conditions.  It  is  only  when 
the  tissues  are  in  a  worn-out  condition,  when  we  are  "  run  down," 
as  we  say,  that  the  parasite  may  obtain  a  foothold  in  the  lungs. 


Microscopic  appearance  of  ordinary  milk 
showing  fat  globules  and  bacteria.  The 
cluster  of  bacteria  on  left  side  are  lactic- 
acid-forming  germs.  Tuberculosis  germs 
are  sometimes  found  in  milk. 


HOW  PLANTS  BENEFIT  AND   HARM   MANKIND    181 

Even  if  the  disease  gets  a  foothold,  it  is  quite  jwssible  to  cure  it  if 
it  is  taken  in  time.  The  germ  of  tuberculosis  is  killed  by  exposure 
to  bright  sunlight  and  fresh  air.  Thus  the  course  of  the  disease 
may  be  arrested,  and  a  permanent  cure  Ijrought  alx)ut,  by  a  life 
in  the  open  air,  the  patient  sleeping  out  of  doors,  taking  plenty  of 
nourishing  food  and  very  little  exercise.  See  also  C'hapter  XXIX. 
Typhoid  Fever.  —  One  of  the  most  common  germ  diseases  in 
this  country  and  Europe  is  typhoid  fever.  This  is  a  disease  which 
is  conveyed  by  means  of  water  and  food,  especially  milk,  oysters, 


How  sewage  containing  typhoid  bacteria  may  get  into  drinking  water  :  c,  cesspool  ; 
Im,  layer  of  rock  ;  w,  wash  water. 


and  uncooked  vegetables.  Typhoid  fever  germs  live  in  the  intes- 
tine and  give  off  a  toxin  or  poison  which  gets  into  the  blood,  thus 
causing  the  fever  characteristic  of  the  disease.  The  germs  multi- 
ply very  rapidly  in  the  intestine  and  are  passed  off  from  the  body 
with  the  excreta  from  the  food  tube.  If  these  germs  get  into  the 
water  supply  of  a  town,  an  epidemic  of  typhoid  will  result.  Among 
the  recent  epidemics  caused  by  the  use  of  water  containing  typhoid 
germs  have  been  those  in  Butler,  Pa.,  where  1364  persons  were 
made  ill;  Ithaca,  N.Y.,  with  1350  cases;  and  Watertown,  N.Y., 
where  over  5000  cases  occurred.  Another  source  of  infection  is 
milk.  Frequently  epidemics  have  occurred  which  were  confined  to 
users  of  milk  from  a  certain  dairy.  Upon  investigation  it  was  found 
that  a  case  of  typhoid  had  occurred  on  the  farm  where  the  milk 
came  from,  that  the  germs  had  washed  into  the  well,  and  that  this 


182    HOW  PLANTS  BENEFIT  AND  HARM   MANKIND 

water  was  used  to  wash  the  milk  cans.  Once  in  the  milk,  the  bac- 
teria multiplied  rapidly,  so  that  the  milkman  gave  out  cultures  of 
typhoid  in  his  milk  bottles.  Proper  safeguarding  of  our  water  and 
milk  supply  is  necessary  if  we  are  to  keep  typhoid  away. 

Tetanus,  or  Blood  Poisoning.  —  The  bacterium  causing  blood 
poisoning  is  another  toxin-forming  germ.  It  lives  in  the  earth  and 
enters  the  body  through  cuts  or  bruises.  It  seems  to  thrive  best 
in  less  oxygen  than  is  found  in  the  air.  It  is  therefore  important 
not  to  close  up  with  court-plaster  wounds  in  which  such  germs  may 
have  found  lodgment.  It,  with  typhoid,  is  responsible  for  four 
times  as  many  deaths  as  bullets  and  shells  in  time  of  battle.  The 
wonderfully  small  death  rate  of  the  Japanese  army  in  their  war  with 
Russia  was  due  to  the  fact  that  the  Japanese  soldiers  always  boiled 
their  drinking  water  before  using  it,  and  their  surgeons  always 
dressed  all  wounds  on  the  battlefield,  using  powerful  antiseptics  in 
order  to  kill  any  bacteria  that  might  find  lodgment  in  the  exposed 
wounds. 

Other  Diseases.  —  Many  other  diseases  have  been  traced  to 
bacteria.  Diphtheria  is  one  of  the  best  known.  As  it  is  a  throat 
disease,  it  may  easily  be  conveyed  from  one  person  to  another  by 
kissing,  putting  into  the  mouth  objects  which  have  come  in  con- 
tact with  the  mouth  of  the  patient  having  diphtheria,  or  by  food 
into  which  the  germs  have  been  carried.  Another  disease  which 
probably  causes  more  misery  in  the  world  than  any  other  germ 
disease  is  syphilis.  It  is  estimated  that  80  per  cent  of  blindness 
in  newborn  children  is  due  to  this  cause.  Grippe,  pneumonia, 
whooping  cough,  and  colds  are  believed  to  be  caused  by  bacteria. 
Other  diseases,  as  malaria,  yellow  fever,  sleeping  sickness,  and 
probably  smallpox,  scarlet  fever,  and  measles,  are  due  to  the 
attack  of  one-celled  animal  parasites.  Of  these  we  shall  learn 
later  in  the  chapter  on  Protozoa. 

Methods  of  fighting  Germ  Diseases.  —  As  we  have  seen,  dis- 
eases produced  by  bacteria  may  be  caused  by  the  bacteria  being 
transferred  from  one  person  directly  to  another,  or  the  disease  may 
obtain  a  foothold  in  the  body  from  food,  water,  by  breathing  in  the 
germs  in  the  air,  or  by  taking  them  into  the  blood  through  a  cut  or 
a  wound  or  a  body  opening. 

It  is  evident  that  as  individuals  we  may  each  do  something  to 


HOW  PLANTS  BENEFIT  AND   HARM   MANKIND    183 

prevent  the  spread  of  germ  diseases,  especially  in  our  homes.  We 
may  keep  our  bodies,  especially  our  hands  and  faces,  clean.  Sweeping 
and  dusting  may  be  done  with  damp  cloths  so  as  not  to  raise  a 
dust;  our  milk  and  water,  when  from  a  suspicious  supply,  should  be 
sterilized,  —  that  is,  the  germs  contained  killed  by  boiling  or  pasteur- 
izing for  a  few  minutes.  Wounds  through  which  bacteria  might 
obtain  foothold  in  the  body  should  be  washed  with  some  antiseptic, 
a  substance  like  corrosive  sublimate  (1  part  to  1000  water)  or 
carbolic  acid  (1  part  to  40  water),  which  kills  the  germs.  In  a 
later  chapter  we  shall  learn  more  of  how  we  may  cooperate  with  the 
authorities  to  combat  disease  and  make  our  city  or  town  a  better 
place  to  live  in.^ 

Reference  Books 

elementary 

Sharpe,  A  Laboratory  Manual  for  the  Solution  of  Problems  in  Biology.    American 

Book  Company. 
Conn,  Bacteria,  Yeasts,  and  Molds  in  the  Home.    Ginn  and  Company. 
Conn,  Story  of  Germ  Life.     D.  Appleton  and  Company. 
Davison,  The  Human  Body  and  Health.     American  Book  Company. 
Frankland,  Bacteria  in  Daily  Life.     Longmans,  Green,  and  Company. 
Prudden,  Dust  and  its  Dangers.     G.  P.  Putnam's  Sons. 
Prudden,  The  Story  of  the  Bacteria.     G.  P.  Putnam's  Sons. 
Ritchie,  Primer  of  Sanitation.    Worid  Book  Company. 

ADVANCED 

Conn,  Agricultural  Bacteriology.    P.  Blakiston's  Sons  and  Company. 

Coulter,  Barnes,  and  Cowles,  A  Textbook  of  Botany,  Vol.  I.  American  Book  Com- 
pany. 

De  Bary,  Comparative  Morphology  and  Biology  of  the  Fungi,  Mycetozoa,  and  Bacteria 
Clarendon  Press. 

Duggar,  Fringous  Diseases  of  Plants.     Ginn  and  Company. 

Hough  and  Sedgwick,  The  Human  Mechanism.     Ginn  and  Company. 

Muir  and  Ritchie,  Maniud  of  Bacteriology.     The  Macmillan  Company. 

Newman,  The  Bacteria.     G.  P.  Putnam's  Sons. 

Sedgwick,  Principles  of  Sanitary  Science  and  Public  Health.  The  Macmillan  Com 
pany. 

»  Teachers  may  take  up  parts  or  all  of  Chapter  XXIX  at  this  point.  I  have 
found  it  advisable  to  repeat  much  of  the  work  on  bacteria  after  the  students 
have  taken  up  the  study  of  the  human  organism. 


XIV.   THE  RELATIONS   OF  PLANTS  TO  ANIMALS 

Problem  XXIV,  TJie  general  hiological  relations  existing  he- 
tiveen  plant  sand  aniinals.    {Labor  abory  Manual,  Proh.  XXIV.) 

(a)  A  balanced  aquarUnn. 

(b)  Relations  between  green  filants  and  animals, 

(c)  The  nitrogen  cycle, 
id)  A  hay  infusion. 

Study  of  a  Balanced  Aquarium.  —  Perhaps  the  best  way  for  us 
to  understand  the  interrelation  between  plants  and  animals  is  to 
study  an  aquarium  in  which  plants  and  animals  live  and  in  which 
a  balance  has  been  established  between  the  plant  life  on  one  side 
and  animal  life  on  the  other.  Aquaria  containing  green  pond 
weeds,  either  floating  or  rooted,  a  few  snails,  some  tiny  animals 
known  as  water  fleas,  and  a  fish  or  two  will,  if  kept  near  a  light 
window,  show  this  relation. 

We  have  seen  that  green  plants  under  favorable  conditions  of 
sunlight,  heat,  moisture,  and  with  a  supply  of  raw  food  materials, 
give  off  oxygen  as  a  by-product  while  manufacturing  food  in  the 
green  cells.  We  know  the  necessary  raw  materials  for  starch 
manufacture  are  carbon  dioxide  and  water,  while  nitrogenous 
material  is  necessary  for  the  making  of  proteids  within  the  plant. 
In  previous  experiments  we  have  proved  that  carbon  dioxide  is 
given  off  by  any  living  thing  when  oxidation  occurs  in  the  body. 
The  crawling  snails  and  the  swimming  fish  give  off  carbon  dioxide, 
which  is  dissolved  in  the  water ;  the  plants  themselves,  night  and 
day,  oxidize  food  within  their  bodies,  and  so  must  pass  off  some 
carbon  dioxide.  The  green  plants  in  the  daytime  use  up  the 
carbon  dioxide  obtained  from  the  various  sources  and,  with  the 
water  taken  in,  manufacture  starch.  While  this  process  is  going 
on,  oxygen  is  given  off  to  the  water  of  the  aquarium,  and  this  free 
oxygen  is  used  by  the  animals. 

But  the  plants  are  continually  growing  larger.  The  snails  and 
fish,  too,  eat  parts  of  the  plants.     Thus  the  plant  life  gives  food 

184 


THE  RELATIONS  OF  PLANTS  TO  .VNIMALS      185 

to  at  least  part  of  the  animal  life  within  the  aquarium.  The  ani- 
mals give  off  certain  nitrogenous  wastes  of  which  we  shall  learn 
more  later.  These  materials,  with  other  nitrogenous  matter  from 
the  dead  parts  of  the  plants  or  animals,  form  the  part  of  the  raw 
material  of  the  proteid  food  manufactured  within  the  plant.  The 
animals  eat  the  plants  and  give  off  organic  waste,  from  which  the 


A  balanced  aquarium. 


plants  make  their  food  and  living  matter.  The  plants  give  off 
oxygen  to  the  animals,  and  the  animals  give  carbon  dioxide  to  the 
plants.  Thus  a  balance  exists  between  the  plants  and  animals 
in  the  aquarium. 

Relations  between  Green  Plants  and  Animals.  —  What  goes 
on  in  the  aquarium  is  an  example  of  the  relation  existing  between 
all  green  plants  and  all  animals.  Everywhere  in  the  world  green 
plants  are  making  food  which  becomes,  sooner  or  later,  the  food  of 


186     THE   RELATIONS  OF   PLANTS  TO   ANIMALS 

animals.  Man  may  not  feed  upon  the  leaves  of  plants,  but  he  eats 
fruits  and  seeds  in  one  form  or  another.  Even  if  he  does  not  feed 
directly  upon  plants,  he  eats  the  flesh  of    herbivorous  animals, 


Carbon  dioxide 
(CO2) 


Carbon  dioxide 

>i  (CO2) 


Simple  Salts 


Plants 

with  chlorophyll 

buildup  complex 

organic  substances 

They  store  up 

energy  from  the  sun 

in  the  process 

and 


form 
lorganic 
food  of 


Animals 

and  plants  without 

chlorophyll 

which  tear  down  complex^  Ammonia 

organic  substances       I     (NH3) 

and  set  free  energy 

in  the  process  in 

form  of  heat 


Energy  from  sub.  Energy  set  free 

as  heat. 

The  relations  between  green  plants  and  animals. 


which  in  turn  feed  directly  upon  plants.  And  so  it  is  the  world 
over;  the  plants  are  the  food-makers  and  supply  the  animals. 
Green  plants  also  give  a  very  considerable  amount  of  oxygen  to 
the  atmosphere  every  day,  which  the  animals  may  make  use  of. 

The  Nitrogen  Cycle.  — 

^Animal  Life 

)sing  Bacteria 


The  animals  in  their  turn 
supply  much  of  the  carbon 
dioxide  that  the, plant  uses 
in  starch-making.  They 
also  supply  most  of  the 
nitrogenous  matter  used 
by  the  plants,  part  being 
given  the  plants  from  the 
dead  bodies  of  their  own 
relatives  and  part  being 
released  through  the  agency  of  bacteria,  which  live  upon  the  roots 
of  certain  plants.  These  bacteria  are  the  only  organisms  that 
can  take  nitrogen  from  the  air.  Thus,  in  spite  of  all  the  nitrogen 
of  the  atmosphere,  plants  and  animals  are  limited  in  the  amount 


Nitrites 
■■s     Nitric  Bacteria 

The  nitrogen  cycle. 


THE  RELATIONS   OF  PLANTS  TO  ANIMALS     187 


available.  And  the  available  supply  is  used  over  and  over  again, 
perhaps  in  nitrogenous  food  by  an  animal,  then  it  may  be  given 
off  as  organic  waste,  get  into  the  soil,  and  ])e  taken  up  by  a 
plant  through  the  roots.  Eventually  the  nitrogen  forms  part  of 
the  food  supi)ly  in  the  body  of  the  plant,  and  then  may  become 
part  of  its  living  matter.  When  the  plant  dies,  the  nitrogen  is 
returned  to  the  soil.  Thus  the  usable  nitrogen  is  kept  in  cor- 
relation. 

Symbiosis.  —  Plants  and  animals  are  seen  in  a  general  way  to  be 
of  mutual  advantage  to  each  other.  Some  plants,  called  lichens, 
show  this  mutual 
partnership  in  the  fol- 
lowing interesting  way. 
A  lichen  is  composed 
of  two  kinds  of  plants, 
one  at  least  of  which 
may  live  alone,  but 
which  have  formed  a 
partnership  for  life, 
and  have  divided  the 
duties  of  such  life  be- 
tween them.  In  most 
lichens  the  alga,  a  green 
plant,  forms  starch  and 
nourishes  the  fungus. 
The  fungus,  in  turn,  produces  spores,  by  means  of  which  new  lichen^ 
are  started  in  life.     The  body  of  the  lichen  is   usually  protected 

by  the  fungus,  which  is  stronger  in 
structure  than  the  green  part  of  the 
combination.  This  process  of  living 
together  for  mutual  advantage  is  called 
symbiosis.  Some  animals  thus  com- 
bine with  plants;  for  example,  the 
tiny  animal  known  as  the  hydra  with 
certain  of  the  one-celled  algse,  and,  if 
we  accept  the  term  in  a  wide  sense,  all  green  plants  and  animals 
live  in  this  relation  of  mutual  give  and  take.  Animals  also 
frequently  live  in  this  relation  to  each  other,  as  the  crab,  which 


A  lichen  {Physcia  slellaris).    Photographed  by 
W.  C.  Barbour. 


Stages  in  the  formation  of  the 
lichen  thallus,  showing  the  re- 
lation of  the  threadlike  fungus 
to  the  green  cells  of  the  alga. 
(After  Bornet.) 


188     THE   RELATIONS   OF   PLANTS  TO  ANIMALS 


lives  within  the  shell  of  the  oyster ;  the  sea  anemones,  which  are 
carried  around  on  the  backs  of  some  hermit  crabs,  aiding  the 
crab  in  protecting  it  from  its  enemies,  and  being  carried  about 
by  the  crab  to  places  where  food  is  plentiful. 
•  A  Hay  Infusion.  —  Still  another  example  of  the  close  relation 
between  plants  and  animals  may  be  seen  in  the  study  of  a  hay 


Life  in  a  late  stage  of  a  hay  infusion.  B,  bacteria,  swimming  or  forming  masses 
of  food  upon  which  the  one-celled  animals,  the  paramoecia,  are  feeding  ;  G, 
gullet;  F.V.,  food  vacuole;  C.V.,  contractile  vacuole;  P,  pleuococcus ;  P.D., 
pleurococcus  dividing. 

infusion.  If  we  place  a  wisp  of  hay  or  straw  in  a  small  glass  jar 
nearly  full  of  water,  and  leave  it  for  a  few  days  in  a  warm  room, 
certain  changes  are  seen  to  take  place  in  the  contents  of  the  jar; 
the  water  after  a  little  while  gets  cloudy  and  darker  in  color,  and  a 
scum  appears  on  the  surface.  If  some  of  this  scum  is  examined 
under  the  compound  microscope,  it  will  be  found  to  consist  almost 
entirely  of  bacteria.  These  bacteria  evidently  aid  in  the  decay 
which  (as  the  unpleasant  odor  from  the  jar  testifies)  is  taking  place. 
As  we  have  learned,  bacteria  flourish  wherever  the  food  supply  is 


THE   RELATIONS   OF  PLANTS   TO   ANIMALS      189 

abundant.  The  water  within  the  jar  has  come  to  contain  much  of 
the  food  material  which  was  once  within  the  leaves  of  the  grass,  — 
organic  nutrients,  starch,  sugar,  and  proteids,  formed  in  the  leaf 
by  the  action  of  the  sun  on  the  chlorophyll  of  the  leaf,  and  now 
released  into  the  water  by  the  breaking  down  of  the  walls  of  the 
cells  of  the  leaves.  The  bacteria  themselves  release  this  food  from 
the  hay  by  causing  it  to  decay.  After  a  few  days  small  one- 
celled  animals  appear;  these  multiply  with  wonderful  rapidity,  so 
that  in  some  cases  the  surface  of  the  water  seems  to  be  almost  white 
with  active  one-celled  forms  of  life.  If  we  ask  ourselves  where 
these  animals  come  from,  we  are  forced  to  the  conclusion  that  they 
must  have  been  in  the  water,  in  the  air,  or  on  the  hay.  Hay  is 
dried  grass,  which  may  have  been  cut  in  a  field  near  a  pool  con- 
taining these  creatures.  When  these  pools  dried  up,  the  wind 
may  have  scattered  some  of  these  little  organisms  in  the  dried 
mud. or  dust.  Some  may  exist  in  a  dormant  state  on  the  hay, 
the  water  serving  to  awaken  them  to  active  life.  In  the  water, 
too,  there  may  have  been  some  living  cells,  plant  and  animal. 

At  first  the  multipUcation  of  the  tiny  animals  within  the  hay 
infusion  is  extremely  rapid ;  there  is  food  in  abundance  and  near 
at  hand.  After  a  few  days  more,  however,  several  kinds  of  one- 
celled  animals  may  appear,  some  of  which  prey  upon  others.  Con- 
sequently a  struggle  for  life  begins,  which  becomes  more  and  more 
intense  as  the  food  from  the  hay  is  used  up.  Eventually  the  end 
comes  for  all  the  animals  unless  some  green  plants  obtain  a  foot- 
hold within  the  jar.  If  such  a  thing  ha  opens,  food  will  be  manu- 
factured witnin  their  bodies,  a  new  food  supply  arises  for  the 
animals  within  the  jar,  and  a  balance  of  life  results. 

Reference  Books 

elementary 

Sharpe,  A  Laboratory  Manual  for  the  Solution  of  Problems  in  Biology.    American 
Book  Company. 

ADVANCED 

Eggerling  and  Ehrenberg,  The  Fresh  Water  Aquarium  and  its  Inhabitants.     Henry 

Holt  and  Company. 
Furneaux,  Life  in  Ponds  and  Streams. 
Parker,  Biology.     The  Macmillan  Company. 


XV.  THE   PROTOZOA 

Problem  XXV.    The  study  of  a  one-celled  animal.    {Laboror 
tory  Manual,  Problem  XXV.) 
(a)  In  Us  relations  to  its  surroundings. 
(Jb)  As  a  cell.    {Optional.) 
(c)  In  its  relations  to  man. 

We  have  seen  that  perhaps  the  simplest  plant  would  be  exem- 
phfied  by  one  of  the  tiny  bacteria  we  have  just  read  about.  A 
typical  one-celled  plant,  however,  would  contain  green  coloring 
matter  or  chlorophyll,  and  would  have  the  power  to  manufacture 
its  own  food  under  conditions  giving  it  a  moderate  temperature, 
a  supply  of  water,  oxygen,  carbon  dioxide,  and  sunlight.  Such  a 
simple  plant  is  the  pleurococcus,  the  *'  green  slime  "  seen  on  the 
shady  sides  of  trees,  stones,  or  city  houses.  This  plant  would  meet 
one  definition  of  a  cell,  as  it  is  a  minute  mass  of  protoplasm  contain- 
ing a  nucleus.  It  is  surrounded  by  a  wall  ^  of  a  woody  material 
which  covers  a  delicate  membrane  formed  by  the  activity  of 
the  living  matter  within  the  cell.  It  also  contains  granules  of 
protoplasm  colored  green,  called  chloroplasts.  Of  their  part  in 
the  manufacture  of  organic  food  we  have  already  learned.  Such 
is  a  simple  plant  cell.  Let  us  now  examine  a  simple  animal  cell  in 
order  to  compare  it  with  that  of  a  plant. 

The  Paramoecium.  —  The  one-celled  animal  most  frequently 
found  in  hay  infusions  is  the  paramoecium,  or  slipper  animalcule 
(so-called  because  of  its  shape). 

This  cell  is  elongated,  oval,  or  elliptical  in  outline,  but  somewhat 
flattened.  Seen  under  the  low  power  of  the  microscope,  it 
appears  to  be  extremely  active,  rushing  about  now  rapidly,  now 
more  slowly,  but  seemingly  always  taking  a  definite  course.  The 
more  pointed  end  of  the  body  (the  anterior)  usually  goes  first. 

1  This  shows  one  practical  reason  why  plant  food  often  contains  more  indigestible 
matter  than  animal  food  of  same  bulk. 

190 


THE  PROTOZOA 


101 


If   it    pushes    its  way  past  any  dense    substance    in    the  water, 
the  cell  body  is  seen  to  change  its  shape  as  it  squeezes  through. 

The  cell  body  is  almost  transparent,  and  consists  of  semifluid 
protoplasm  which  has  a  granular  grayish  appearance  under  the 
microscope.  This  protoplasm  appears  to  be  bounded  by  a  very 
delicate  membrane  through  which  project  numerous  delicate  threads 
of  protoplasm  called  cilia.  (These  are 
usually  invisible  under  the  microscope.) 

The  locomotion  of  the  paramoecium  is 
caused  by  the  movement  of  these  ciha  which 
lash  the  water  like  a  multitude  of  tiny  oars. 
The  cilia  also  send  tiny  particles  of  food  into 
a  funnel-like  opening,  the  gullet  on  one  side 
of  the  cell.  Once  within  the  cell  body,  the 
particles  of  food  materials  are  gathered  into 
little  balls  within  the  almost  transparent 
protoplasm.  These  masses  of  food  seem  to 
be  inclosed  within  a  little  area  containing 
fluid,  called  a  vacuole.  Other  vacuoles 
appear  to  be  clear;  these  are  spaces  in 
which  food  has  been  digested.  One  or 
two  larger  vacuoles  may  be  found;  these 
are  the  contractile  vacuoles;  their  purpose 
seems  to  be  to  pass  off  waste  material  from 
the  cell  body.  This  is  done  by  pulsation 
of  the  vacuole,  which  ultimately  bursts,  pass- 
ing fluid  waste  to  the  outside.  Solid  wastes  are  passed  out  of 
the  cell  in  somewhat  the  same  manner.  The  nucleus  of  the  cell 
is  not  easily  visible  in  living  specimens.  In  a  cell  that  has  been 
stained  it  has  been  found  to  be  a  double  structure,  consisting  of 
one  large  and  one  small  portion,  called  respectively  the  macro- 
nucleus  and  the  micronu^leu^. 

Response  to  Stimuli.  —  In  the  paramoecium,  as  in  the  one-celled 
plants,  the  protoplasm  composing  the  cell  can  do  certain  things. 
Protoplasm  responds,  in  both  plants  and  animals,  to  certain  agen- 
cies acting  upon  it,  coming  from  without;  these  agencies  we  call 
stimuli.  Such  stimuli  may  be  light,  differences  of  temperature, 
presence  of  food,  electricity,  or  other  factors  of  its  surroundings. 


Paramoecium.  Greatly 
maguified.  From  side. 
F.V.,  food  vacuole ;  C.F., 
contractile  vacuole; 
M,  mouth  ;  A^,  nucleus ; 
W.V.,  water  vacuole. 
(After  Sedgwick  and 
Wilson.) 


192 


THE  PROTOZOA 


The    original    cell 


Plant  and  animal  cells  may  react  differently  to  the  same  stimuli. 
In  general,  however,  we  know  that  protoplasm  is  irritable  to  some 
of  these  factors.  To  severe  stimuli,  protoplasm  usually  responds 
by  contracting,  another  power  which  it  possesses.  We  know,  too, 
that  plant  and  animal  cell^  take  in  food  and  change  the  food  to 
protoplasm,  that  is,  that  they  assimilate  food;  and  that  they 
may  waste  away  and  repair  themselves.  Finally,  we  know  that 
new  plant  and  animal  cells  are  reproduced  from  the  original  bit  of 
protoplasm,  a  single  cell. 

Reproduction    of    Paramoecium.  —  Sometimes    a    paramoecium 
may  be  found  in  the  act  of  dividing  by  the  process  known  as  fission, 

to  form  two  new  cells,  each  of  which  contains 

half  of  the  original    cell.     This  is  a  method 

of    asexual    reproduction. 

may  thus  form  in  succes- 
sion   many    hundreds    of 

cells  in  every  respect  like 

the  original  parent  cell. 
Frequently     another 

method    of    reproduction 

may  be    observed.      This 

is  called  conjugation,  and 

somewhat    resembles   the 

same  process  in  the  simple 

plants.    Two  cells  of  equal 

size     attach      themselves 

together  as  shown  in  the 

Figure.  Complicated 
changes  take  place  in  the  nuclei  of  the  two  cells  thus  united, 
which  results  in  an  equal  exchange  of  part  of  the  material 
forming  the  nucleus.  After  a  short  period  of  rest  the  two  cells 
separate.  The  stage  of  conjugation  we  believed  in  the  plants  to 
be  a  sexual  stage.  There  seems  every  reason  to  believe  that  it 
is  a  Hke  stage  in  the  Hfe  history  of  the  paramoecium. 

Amceba.  —  In  order  to  understand  more  fully  the  life  of  a  simple 
bit  of  protoplasm,  let  us  take  up  the  study  of  the  amoeba,  a  type 

1  Amoebae  may  be  obtained  from  the  hay  infusion,  from  the  dead  leaves  in  the  bot- 
tom of  small  pools,  from  the  same  source  in  fresh-water  aquaria,  from  the  roots  of 


MAC 
MIC 


Paramoecium  divid- 
ing by  fission. 
Greatly  magnified. 
M,  mouth;  MAC, 
mac  ronucleus  ; 
Af  7C,  micronucleus. 
(After  Sedgwick 
and  "Wilson.) 


Paramoecium.  Greatly 
magnified.  M, 
mouth ;  MIC,  micro- 
nucleus;  MAC,  ma- 
cronucleus ;  C  V,  con- 
tractile  vacuole. 
(After  Sedgwick  and 
Wilson.) 


THE  PROTOZOA 


193 


of  the  simplest  form  of  life  known,  either  plant  or  animal.  Unlike 
the  plant  and  animal  cells  we  have  examined,  the  amoeba  has  no 
fixed  form.  Viewed  under  the  compound  microscope,  it  has  the 
appearance  of  an  irregular  mass  of  granular  protoplasm.  Its  form 
is  constantly  changing  as  it  moves  about.  This  is  due  to  the  push- 
ing out  of  tiny  projections  of  the  protoplasm  of  the  cell,  called 
pseiidopodia  (false  feet).  The 
outer  layer  of  protoplasm  is 
not  so  granular  as  the  inner 
part;  this  outer  layer  is 
called    ectoplasm,    the   inside 


AnicL'ba,  with  pseudopodia  (7^)  ex- 
tended;  EC,  ectoplasm;  END, 
endoplasm ;  the  dark  area  (A'^.) 
is  the  nucleus.  From  photo- 
graph loaned  by  Professor  G.  N. 
Calkins. 


Aniceba,  showing  the  changes  which  take 
place  during  division.  The  dark  body 
in  each  Figure  is  the  nucleus ;  the  trans- 
parent drcle,  the  contractile  vacuole ; 
the  outer,  clear  portion  of  the  body  the 
ectoplasm ;  the  granular  portion,  the 
endoplasm ;  the  granular  masses,  food 
vacuoles.     Much  magnified. 


l)eing  called  endoplasm.  In  the  central  part  of  the  cell  is  the 
nucleus.  This  important  organ  is  difficult  to  see,  except  in  cells 
that  have  been  stained. 

The  locomotion  is  accomplished,  according  to  Professor  Jennings 
of  Johns  Hopkins  University,  by  a  kind  of  roUing  motion,  "  the 
upper  and  lower  surfaces  constantly  interchanging  positions.'* 
The  pseudopodia  are  pushed  forward  in  the  direction  which  the 
animal  is  to  go,  the  rest  of  the  body  following. 

duckweed  or  other  small  water  plants,  or  from  green  al^ae  growing  in  quiet  localities. 
No  awe  method  of  obtaining  them  can  be  given. 
HUNT.  ES.  BIO. 13 


194  THE  PROTOZOA 

Although  but  a  single  cell,  still  the  amoeba  appears  to  be  aware 
of  the  existence  of  food  when  food  is  near  at  hand.  Food  may  be 
taken  into  the  body  at  any  point,  the  semifluid  protoplasm  simply 
rolling  over  and  engulfing  the  food  material.  Within  the  body, 
as  in  the  paramoecium,  the  food  is  inclosed  within  a  fluid  space  or 
vacuole.  The  protoplasm  has  the  power  to  take  out  such  material 
as  it  can  use  to  form  new  protoplasm  or  give  energy.  It  will  then 
rid  itself  of  any  material  that  it  cannot  use.  Thus  it  has  the  power 
of  selective  absorption,  a  character  found  in  the  protoplasm  of 
plants  previously  studied.  Circulation  of  food  material  is  accom- 
plished by  the  constant  streaming  of  the  protoplasm  within  the 
cell. 

The  cell  absorbs  oxygen  from  the  water  by  osmosis  through 
its  delicate  membrane,  giving  up  carbon  dioxide  in  return.  Thus 
the  cell  ''  breathes  "  through  any  part  of  its  body  covering. 

Waste  products  formed  from  the  oxidations  which  take  place 
in  the  cell  are  passed  out  by  means  of  the  contractile  vacuole. 

The  amoeba,  like  other  one-celled  organisms,  reproduces  by  the 
process  of  fission.  A  single  cell  divides  by  splitting  into  two  others, 
each  of  which  resembles  the  parent  cell,  except  that  they  are  of 
less  bulk.  When  these  become  the  size  of  the  parent  amoeba, 
they  in  turn  each  divide.     This  is  a  kind  of  asexual  reproduction. 

When  conditions  unfavorable  for  life  come,  the  amoeba,  like 
some  one-celled  plants,  encysts  itself  within  a  membranous  wall. 
In  this  condition  it  may  become  dried  and  be  blown  through  the 
air.  Upon  return  to  a  favorable  environment,  it  begins  life  again, 
as  before.     In  this  respect  it  resembles  the  spore  of  a  plant. 

From  the  study  of  the  amcebalike  organisms  which  are  known  to  cause 
malaria,  and  by  comparison  with  the  amoebae  which  live  in  our  ponds 
and  swamps,  it  seems  likely  that  every  amoeba  has  a  complicated  life 
history  during  which  it  passes  through  a  sexual  stage  of  existence. 

The  Cell  as  a  Unit.  —  In  the  daily  life  of  a  one-celled  animal  we 
find  the  single  cell  performing  all  the  general  activities  which  we 
shall  later  find  the  many-celled  animal  is  able  to  perform.  In  the 
amoeba  no  definite  parts  of  the  cell  appear  to  be  set  off  to  perform 
certain  functions;  but  any  part  of  the  cell  can  take  in  food,  can 
absorb  oxygen,  can  change  the  food  into  protoplasm  and  excrete 


THE  PROTOZOA 


195 


the  waste  material.  The  single  cell  is,  in  fact,  an  organism  able 
to  carry  on  the  business  of  Hving  as  effectually  as  a  very  complex 
animal. 

Complex  One-celled  Animals.  —  In  the  paramoecium  we  find  a 
single  cell,  but  we  find  certain  parts  of  the  cell  having  certain  definite 
functions  :  the  cilia  are  used  for  locomotion ;  a  definite  part  of  the  cell  takes 
in  food,  while  the  waste  passes 
out  at  another  definite  spot. 
In  another  one-celled  animal 
called  vorticella,  part  of  the 
cell  has  become  elongated 
and  is  contractile.  By  this 
stalk  the  little  animal  is 
fastened  to  a  water  plant 
or  other  object.  The  stalk 
may  be  said  to  act  like  a 
muscle  fiber,  as  its  sole  func- 
tion seems  to  be  movement ; 
the  cilia  are  located  at  one 
end  of  the  cell  and  serve  to 
create  a  current  of  water 
which  will  bring  food  par- 
ticles to  the  mouth.  Here 
we  have  several  parts  of  the 
cell  each  doing  a  different 
kind  of  work.  This  is  known 
as  physiological  division  of 
labor. 


Photograph  of  a  living  bell  animalcule  (vorti- 
cella) enlarged  two  hundred  diameters.  Notice 
the  contractile  stalk  and  the  circle  of  cilia 
about  the  mouth. 


Habitat  of  Protozoa.  —  Protozoa  are  found  almost  everywhere 
in  shallow  water,  seemingly  never  at  any  great  depth.  They  ap- 
pear to  be  attracted  near  to  the  surface  by  light  and  the  supply  of 
oxygen.  Every  fresh-water  lake  swarms  with  them;  the  ocean  con- 
tains countless  myriads  of  many  different  forms. 

Use  as  Food.  —  They  are  so  numerous  in  lakes,  rivers,  and  the 
ocean  as  to  form  the  food  for  many  animals  higher  in  the  scale  of 
life.  Almost  all  fish  that  do  not  take  the  hook  and  that  travel 
in  schools,  or  companies,  migrating  from  one  place  to  another, 
live  partly  on  such  food.  Many  feed  on  slightly  larger  animals, 
which  in  turn  eat  the  Protozoa.  Such  fish  have  on  each  side  of  the 
mouth  attached  to  the  gills  a  series  of  small  structures  looking  like 
tiny  rakes.    These  are  called  the  gill  rakers,  and  aid  in  collecting 


196 


THE   PROTOZOA 


tiny  organisms  from  the  water  as  it  passes  over  the  gills.  The 
whale,  the  largest  of  all  mammals,  strains  protozoans  and  other 
small  animals  and  plants  out  of  the  water  by  means  of  hanging 
plates  of  whalebone,  the  slender  filaments  of  which  form  a  sieve 
from  the  top  to  the  bottom  of  the  mouth. 

Relation  of  Protozoa  to  Disease.  —  The  study  of  the  hfe  history 
and  habits  of  the  Protozoa  has  resulted  in  the  finding  of  many 
parasitic  forms,  and  the  consequent  explanation  of  some  kinds 
of  disease.     One  parasitic  protozoan  like   an   amoeba    is    called 

Plasmodium  malarice.     It  causes 


the  disease  known  as  malaria. 
Part  of  its  life  is  passed  with- 
in the  body  of  a  mosquito  (the 
anopheles),  into  the  stomach 
of  which  it  passes  when  the 
^^l^'^K^^^B^^^^  mosquito  sucks  the  blood  from  a 

^^^^^»VP^^H^^         person  having  malaria.     Within 
^H^|E^^^        ^I^^^B         the  body  of  the  mosquito  a  com- 
^S^j^^^w^^^  ^^^^         plicated  part  of  the  life  history 
^^^^^^^^1     ^^^H        takes  place,  which  results  in  a 

stage  of  the  parasite  establish- 
ing itself  within  the  glands  which 
secrete  the  saliva  of  the  mos- 
quito. When  the  mosquito 
pierces  its  human  prey  a  second 
time,  some  of  the  parasites  are 
introduced  into  the  blood  along  with  the  saliva.  These  para- 
sites enter  the  corpuscles  of  the  blood,  increase  in  size,  and  then 
form  spores.  The  rapid  process  of  spore  formation  results  in 
the  chill  of  malaria.  Later,  when  the  spores  almost  fill  the  blood 
corpuscle,  it  bursts,  and  the  parasites  enter  the  fluid  portion  of  the 
blood.  There  they  release  a  poison  which  causes  the  fever.  The 
spores  may  again  enter  the  blood  corpuscles  and  in  forty-eight  or 
seventy-two  hours  repeat  the  process  thus  described.  Yellow 
fever  is  undoubtedly  conveyed  by  another  species  of  mosquito, 
and  is  probably  due  to  the  presence  of  a  protozoan  similar  to 
that  of  malaria  in  the  blood.  That  these  diseases  may  be  stamped 
out  by  the  destruction  of  the  mosquitoes,  by  preventing  their  breed- 


Blood  corpuscles  of  a  patient  with 
malarial  fever.  Two  corpuscles  con- 
tain the  parasites.  Photograph, 
greatly  enlarged,  by  Davison. 


THE  PROTOZOA 


197 


ing  in  swamps  with  the  use  of  oil,  by  draining  the  swamps,  or  by 
the  introduction  of  fish  which  eat  the  mosquito  larva?  has  been 
proved  from  our  experiences  along  the  Panama  Canal,  in  the 
Philippines,  in  Cuba,  and  in  New  Orleans. 

Many  other  diseases  of  man  are  probably  caused  by  parasitic 
protozoans.  Dysentery  of  one  kind  appears  to  be  caused  by  the 
presence  of  an  amcebalike  animal  in  the  digestive  tract.  Small- 
pox, rabies,  and  possibly  other  diseases 
may  be  caused  by  the  action  of  these 
little  animals. 

Another  group  of  protozoan  parasites 
are  called  trypanosomes.  One  of  this 
family  lives  in  the  blood  of  native 
African  zebras  and  antelopes;  seem- 
ingly it  does  them  no  harm.  But  if 
one  of  these  parasites  is  transferred 
by  the  dreaded  tsetse  fiy  to  one  of  the 
domesticated  horses  or  cattle  of  the 
colonist  of  that  region,  death  of  the 
animal  results. 

Another  fly  carries  a  specimen  of 
trypanosome  to  the  natives  of  Central 
Africa,  which  causes  "the  dreaded  and 
incurable  sleeping  sickness."  This 
disease  carries  off  more  than  fifty 
thousand  natives  yearly,  and  many 
Europeans  have  succumbed  to  it.  Its 
ravages  are  now  largely  confined  to  an  area  near  the  large 
Central  African  lakes  and  the  Upper  Nile,  for  the  fly  which 
carries  the  disease  flies  near  water,  seldom  going  more  than 
150  feet  from  the  banks  of  streams  or  lakes.  The  British 
government  is  now  trying  to  control  the  disease  in  Uganda  by 
moving  all  the  villages  at  least  two  miles  from  the  lakes  and 
rivers.  Why?  In  this  country  many  fatal  diseases  of  cattle, 
as  "tick,"  or  Texas  fever,  among  cattle  are  probably  caused 
by  protozoans. 

Skeleton  Building.  —  Some  of  the  Protozoa  build  elaborate  skeletons. 
These  may  be  formed  outside  of  the  body,  being  composed  of  tiny  micro- 


How  to  tell  the  common  mos- 
quito iculex),  a,  from  the 
malarial  mosquito  (anopheles), 
b,  when  at  rest.  Note  the 
position  of  body  and  legs. 


198 


THE  PROTOZOA 


scopic  grains  of  sand,  or  other  ma- 
terials. In  some  forms  the  skeleton  is 
internal,  and  may  be  made  of  lime 
which  the  animals  take  out  of  the 
water.  Still  other  Protozoa  construct 
shells  which  house  them  for  a  time ; 
then,  growing  larger,  they  add  more 
chambers  to  their  shell,  forming  ul- 
timately a  covering  of  great  beauty. 
These  shells  or  skeletons  of  Protozoa, 
falling  to  the  sea  bottom,  cover  the 
ocean  floor  to  a  depth  of  several  feet 
in  places. 

The  Protozoa  have  also  played  an 
important  part  in  rock  building.  The 
chalk  beds  of  Kansas  and  other  chalk 
formations  are  made  up  to  a  large  ex- 
tent of  the  tiny  skeletons  of  Protozoa,  called  Foraminifera.  Some  lime- 
stone rocks  are  also  composed  in  large  part  of  such  skeletons. 


Skeleton  of  a  radiolarian.  Highly 
magnified.  From  model  at  Amer- 
ican Museum  of  Natural  History. 


Classification  op  Protozoa 

The  following  are  the  principal  classes  of  Protozoa,  examples  of  which  we  have 

seen  or  read  about :  — 

Class  I.  Rhizopoda  {Gk.= root-footed).  Having  no  fixed  form,  with  pseudopodia. 
Either  naked  as  Amoeba  or  building  limy  (Foraminifera)  or  glasslike  skeletons 
(Radiolaria) . 

Class  II.  Infusoria  (in  infusions).  Usually  active  ciliated  Protozoa.  Examples, 
Paramcecium,  Vorticella. 

Class  III.  Sporozoa  (spore  animals).  Usually  parasitic  and  nonactive.  Exam- 
ple, Plasmodium  malaricB. 

Reference  Books 

elementary 

Sharpe,  A  Laboratory  ManuM  for  the  Solution  of  Problems  in  Biology.     American 

Book  Company. 
Davison,  The  Human  Body  and  Health,  Chap.  XXIV.     American  Book  Company. 
Davison,  Practical  Zoology,  pages  178-184.     American  Book  Company. 
Jordan,  Kellogg,  and  Heath,  Animal  Studies.     D.  Appleton  and  Company- 
Ritchie,  Human  Physiology,  Chap.  XXVI.     World  Book  Company. 


ADVANCED 

Calkins,  G.  N.,  The  Protozoa.     The  MacmUlan  Company. 

Linville  and  Kelly,  General  Zoology,  Chap.  XXI.     Ginn  and  Company. 

Parker,  T.  J.,  Lessons  in  Elementary  Biology.     The  Macmillan  Company. 

Seaman,  L.  S.,  "The  Sleeping  Sickness,"  Outlook,  Jan.  15,  1910. 

Wilson,  E.  B.,  The  Cell  in  Development  and  Inheritance.     The  Macmillan  Company. 


XVI.   THE  METAZOA  — DIVISION   OF   LABOR 

I^ohletn  XXVI,    An  introductory  study  of  many-celled  an- 
imals.   {Laboratory  Manual,  Proh.  XXVI.) 
(a)  Devetopm^ent. 
(.b)  Sponges. 
(c)  TJie  hydra. 

id)  Development  of  tissues  and  organs. 
(e)  Common  functions. 

Reproduction  in  Simple  Plants.  —  Although  there  are  very 
many  plants  and  animals  so  small  and  so  simple  as  to  be  com- 
posed of  but  a  single  cell,  by  far  the  greater  part  of  the  animal 
and  plant  world  is  made  up  of  individuals  which  are  collections  of 
cells  living  together. 

In  a  simple  plant  like  the  pond  scum,  a  string  or  filament  of  cells 
is  formed  by  a  single  cell  dividing  crosswise,  the  two  cells  formed 
give  rise  each  to  two  more,  and  eventually  a  long  thread  of  cells 
results.     Such  growth  of  cells  is  asexual. 

In  some  instances,  however,  a  single  cell  was  formed  by  the  union 
of  two  cells,  one  from  each  of  the  adjoining  filaments  of  the  plant. 
Around  this  cell  eventually  a  hard  coat  was  formed,  and  the  spore^ 
as  it  was  called,  was  thus  protected  from  unfavorable  changes  in 
the  surroundings.  Later,  when  conditions  became  favorable  for 
its  germination,  the  spore  might  form  a  new  filament  of  pond 
scum. 

In  the  seed  plants,  too,  we  found  a  little  plant  within  the  seed 
which,  under  favorable  conditions,  might  give  rise,  through  the 
rapid  multiplication  of  the  cells  forming  it,  to  a  new  plant.  But 
the  plant  within  the  seed  first  arose  from  two  cells,  one  of  which, 
called  a  sperm,  came  from  a  pollen  grain,  the  other  of  which,  the 
egg,  was  found  within  the  embryo  sac  of  the  ovary. 

Reproduction  in  Simple  Animals.  —  In  many-celled  animals, 
as  well  as  many-celled  plants,  the  new  animal  is  formed  by  the 

199 


200 


THE   METAZO A  — DIVISION   OF   LABOR 


union  of  a  sperm  and  an  egg  cell.  A  common  bath  sponge,  an 
earthworm,  a  fish,  or  a  dog,  —  each  and  all  of  them  begin  life  in 
precisely  the  same  way.  Animals  which  are  thus  composed  of 
many  cells  are  known  as  the  Metazoa,  as  distinguished  from  the 
Protozoa,  which  are  made  of  but  a  single  cell. 

Sexual  Development  of  a  Simple  Animal.  —  In  a  many-celled 
animal  the  life  history  begins  with  a  single  cell,  the  fertilized  egg. 
This  cell,  as  we  remember,  has  been  formed  by  the  union  of  two 
other  cells,  a  tiny  (usually  motile)  cell,  the  sperm,  and  a  large  cell, 
the  egg.  After  the  egg  is  fertilized  by  a  sperm  cell,  it  splits  into 
two,  four,  eight,  and  sixteen  cells ;  as  the  number  of  cells  increases, 
a  hollow  ball  of  cells  called  thehlastulais  formed;  later  this  ball  sinks 


•  mm  mm0k  9 


Stages  in  the  segmentation  of  an  egg,  showing  the  formation  of  the  gastrula. 


in  on  one  side,  and  a  double-walled  cup  of  cells,  now  called  a  gas- 
trula, results.  Practically  all  animals  pass  through  the  above 
stages  in  their  development  from  the  egg,  although  these  stages 
are  often  not  plain  to  see  because  of  the  presence  of  food  ma- 
terial (yplk)  in  the  egg.  In  the  sponge  the  gastrula,  which  swims 
by  means  of  cilia,  soon  settles  down,  a  skeleton  is  formed,  other 
changes  take  place,  and  the  sponge  begins  life  as  an  animal 
attached  to  some  support  on  the  water.  The  early  stages  of  life, 
when  an  animal  is  unUke  the  adult,  are  known  as  larval  stages ; 
the  animal  at  this  time  being  called  a  larva. 

The  young  sponge  consists  of  three  layers  of  cells :  those  of  the 
outside,  developed  from  the  outer  layer  of  the  gastrula,  are  called 
ectoderm;  the  inner  layer,  developed  from  the  inner  layer  of  the 
gastrula,  the  endoderm.  A  middle  almost  structureless  layer, 
called  the  mesoderm,  is  also  found.  In  higher  animals  this  layer 
gives  rise  to  muscles  and  parts  of   other  internal  structures. 


THE  METAZOA  — DIVISION  OF  LABOR 


201 


A  horny  fiber  sponge  :  IP,  the  incurrent  pores ; 
O,  osculum.  Notice  that  this  sponge  is  made 
up  of  apparently  several  individuals.  One 
fourth  natural  size. 


The  Structure  of  a  Sponge.  —  The  simplest  kind  of  a  sponge 

has  the  form  of  an  urn,  attached  at  the  lower  end.     A  common 

sponge  living  in  Long  Island  Sound  is  a  tiny  urn-shaped  animal  less 

than  an  inch  in  length.     It 

has  a  skeleton  made  up  of 

very  tiny  spicules  of  lime, 

of    different    shapes.     Cut 

lengthwise,  such  an  animal 

is  seen   to   be   hollow,    its 

body    wall    being    pierced 

with  many   tiny   pores  or 

holes.      The   bath   sponge, 

the    skeleton   of    which    is 

made  up  of  fibers  of  horn, 

or  a  variety  known  as  the 

finger    sponge,    shows    the 

pores  even  better  than  the 

smaller  limy  sponge.     In  a 

bath  sponge,  however,  we  probably  have  a  colony  of  sponges  living 

together.     Each  sponge  has  a  large  number  of  pores  opening  into 

a  central  cavity,  which  in  turn 
opens  by  a  larger  hole,  called  the 
osculum,  to  the  surrounding  water. 
A  microscopic  examination 
shows  the  pores  of  the  sponge 
to  be  lined  on  the  inside  with 
cells  having  a  collar  of  living 
matter  surrounding  a  single  long 
cilium  or  flagellum.  The  flagella, 
lashing  in  one  direction,  set  up 
a  current  of  water  toward  the 
large  inner  cavity.  This  current 
bears  food  particles,  tiny  plants 
and   animals,    which   are  seized 

and  digested  by  the  collared  cells,  these  cells  probably  passing 

on  the  food  to  the  other  cells  of  the  body.     The  jellylike  middle 

layer  of  the  body  is  composed  of  cells  which  secrete  lime  to 

form  the  spicules  and  the  reproductive  cells,  eggs,  and  sperms. 


Diagram  of  a  simple  sponge :  /,  inhalant 
openings ;  0,  exhalant  opening  or 
osculum. 


202 


THE   METAZOA  — DIVISION   OF   LABOR 


The  Hydra.  —  Another  very  simple  animal,  which  unlike  the 
sponge  lives  in  fresh  water/  is  called  the  hydra.  This  little  crea- 
ture is  shaped  like  a  hollow  cylinder  with  a  circle  of  arms  or  ten- 
tacles at  the  free  end.  It  is  found  attached  to  dead  leaves,  sticks, 
stones,  or  water  weed  in  most  fresh-water  ponds.  When  disturbed 
they  contract  it  into  a  tiny  whitish  ball  little  larger  than  the  head 
of  a  pin.     Expanded,  it  may  stretch  its  tentacles  in  search  of  food 

almost  an  inch  from  their 
point  of  attachment.  The 
tentacles  are  provided 
with  batteries  of  minute 
darts  or  stinging  cells,  by 
means  of  which  prey  is 
caught  and  killed.  The 
outer  layer  of  the  animal 
serves  for  protection  as 
well  as  movement  and 
sensation,  certain  cells 
being  fitted  for  each  of 
those  different  purposes. 
Food  Taking.  —  The 
tentacles  then  reach  out 
like  arms,  grasp  the  food, 
and  bend  over  with  it  to- 
ward the  mouth.  Certain 
cells  lining  the  hollow 
body  cavity  pour  out  a 
fluid  which  aids  in  digest- 
ing the  food.  Other  cells  with  long  cilia  circulate  the  food,  while 
still  other  cells  lining  the  cavity  put  out  pseudopodia,  which 
grasp  and  ingest  the  food  particles.  The  tentacles  are  hollow, 
and  the  body  cavity  extends  into  them.  The  outer  layer  of  the 
animal  does  not  digest  the  food,  but  receives  some  of  it  already' 
digested  from  the  inner  layer.  This  food  passes  from  cell  to  cell, 
as  in  plants,  by  osmosis.  The  oxygen  necessary  to  oxidize  the 
food  is  passed  through  the  body  wall,  seemingly  at  any  point,  for 
there  are  no  organs  for  respiration  (breathing). 

1  A  few  sponges,  for  example,  spongilla,  live  in  fresh  water. 


Longitudinal  section  of  a  hydra :  6,  bud ;  ha, 
attached  end ;  m,  mouth ;  ov,  ovary  ;  sp,  sper- 
mary  holding  sperm  cells. 


THE  METAZOA  — DIVISION  OF  LABOR  203 

Reproduction.  —  The  hydra  reproduces  itself  either  by  budding 
or  by  the  production  of  new  animals  by  means  of  eggs  and  sperms, 
sexually.  The  bud  appears  on  the  body  as  a  little  knob,  sometimes 
more  than  one  coming  out  on  the  same  hydra.  At  first  the  bud  is 
part  of  the  parent  animal,  the  body  cavity  extending  into  it.  After 
a  short  time  (usually  a  few  days)  the  young  hydra  separates  from 
the  old  one  and  begins  life  anew.     This  is  asexual  reproduction. 

The  hydra  also  reproduces  by  eggs  and  sperms.  These  sperms 
are  collected  in  little  groups  which  usually  appear  near  the  free 
end  of  the  animal,  the  egg  cells  developing  near  the  base  of  the 
same  hydra.  Both  eggs  and  sperms  grow  from  the  middle  layer 
of  the  animal.  The  sperms,  when  ripe,  are  set  free  in  the  water; 
one  of  them  unites  with  an  egg,  which  is  usually  still  attached  to 
the  body  of  the  hydra,  and  development  begins  which  results  in 
the  growth  of  a  new  hydra  in  a  new  locality. 

The  stages  passed  through  in  development  resemble  closely 
those  already  described  on  page  200,  and  it  would  not  be  hard  to 
imagine  the  gastrula  stage,  turned  upside  down  with  a  circle  of 
tentacles  at  the  open  end.     Our  gastrula  would  then  be  a  hydra. 

Division  of  Labor.  —  If  we  compare  the  amoeba  and  the  para- 
moecium,  we  find  the  latter  a  more  complex  organism  than  the 
former.  An  amoeba  may  take  in  food  through  any  part  of  the 
body ;  the  paramoecium  has  a  definite  gullet ;  the  amoeba  may  use 
any  part  of  the  body  for  locomotion ;  the  paramoecium  has  definite 
parts  of  the  cell,  the  cilia,  fitted  for  this  work.  Since  the  structure 
of  the  paramoecium  is  more  complex,  we  say  that  it  is  a  **  higher  " 
animal.  In  the  vorticella,  a  still  more  complex  cell,  part  of  the 
cell  has  grown  out  like  a  stalk,  has  become  contractile,  and  acts  and 
looks  like  muscle. 

As  we  look  higher  in  the  scale  of  life,  we  invariably  find  that 
certain  parts  of  a  plant  or  animal  are  set  apart  to  do  certain  work, 
and  only  that  work.  Just  as  in  a  community  of  people,  there  are 
some  men  who  do  rough  manual  work,  others  who  are  skilled  work- 
men, some  who  are  shopkeepers,  and  still  others  who  are  profes- 
sional men,  so  among  plants  and  animals,  wherever  collections  of 
cells  live  together  to  form  an  organism,  there  is  division  of  labor, 
some  cells  being  £tted  to  do  one  kind  of  work,  while  others  are 
fitted  to  do  work  of  another  sort. 


204  THE   METAZOA  — DIVISION   OF   LABOR 

As  we  have  seen  in  plants,  this  results  in  a  large  number  of 
collections  of  cells  in  the  body,  each  collection  alike  in  structure  and 
performing  the  same  function.  Such  a  collection  of  cells  we  call 
a  tissue.     (See  Chapter  III.) 

Frequently  several  tissues  have  certain  functions  to  perform  in 
conjunction  with  one  another.  The  arm  of  the  human  body 
performs  movement.  To  do  this,  several  tissues,  as  muscles, 
nerves,  and  bones,  must  act  together.  A  collection  of  tissues  per- 
forming certain  work  is  called  an  organ. 

In  the  sponge,  division  of  labor  occurs  between  the  cells  of  the 
simple  animal,  some  cells  lining  the  incurrent  pores  creating  a 
current  of  water,  and  feeding  upon  the  minute  organisms  which 
come  within  reach,  other  cells  building  the  skeleton  of  the  sponge, 
still  others  becoming  eggs  or  sperms.  Division  of  labor  of  a  more 
complicated  sort  is  seen  in  the  hydra.  Here  the  cells  which  do  the 
same  kind  of  work  are  collected  into  tissues,  each  tissue  being  a 
collection  of  cells,  all  of  which  are  more  or  less  alike  and  do  the 
same  kind  of  work.  But  in  higher  animals  which  are  more 
complicated  in  structure  and  in  which  the  tissues  are  found  work- 
ing together  to  form  organs,  division  of  labor  is  still  more  devel- 
oped. In  the  human  arm,  an  organ  fitted  for  certain  movements, 
think  of  the  number  of  tissues  and  the  complicated  actions  which 
are  possible.  The  most  extreme  division  of  labor  is  seen  in  the 
organism  which  has  the  most  complex  actions  to  perform  and 
whose  organs  are  fitted  for  such  work. 

In  our  daily  life  in  a  town  or  city  we  see  division  of  labor  between 
individuals.  Such  division  of  labor  may  occur  among  other  ani- 
mals, as,  for  example,  bees  or  ants.  But  it  is  seen  at  its  highest 
in  a  great  city  or  in  a  large  business  or  industry.  In  the  stockyards 
of  Chicago,  division  of  labor  has  resulted  in  certain  men  performing 
but  a  single  movement  during  their  entire  day's  work,  but  this 
movement  repeated  so  many  times  in  a  day  has  resulted  in  wonder- 
ful accuracy  and  increased  speed.  Thus  division  of  labor  obtains 
its  end. 

Tissues  in  the  Human  Body.  —  Every  animal  body  above  the 
protozoan  is  composed  of  a  certain  number  of  tissues.  The  cells 
making  up  these  tissues  have  certain  well-defined  characteristics. 
In  very  simple  animals  the  cells  are  all  very  much  alike,  but  in  more 


THE  METAZOA  — DIVISION   OF  LABOR         205 

complex  animals  the  cells  are  more  and  more  unlike  as  their 
work  becomes  more  and  more  differenc.  Let  us  see  what  these  cells 
may  be,  what  their  structure  is,  and,  in  a  general  way,  what  func- 
tion each  has  in  the  human  body. 

Muscle  Cells:  —  A  large  part  of  our  body  is  made  up  of 
muscle.  Muscle  cells  are  elongated  in  shape,  and  have  great  con- 
tractile power.  Their  work  is  that  of  causing  movement,  and  this 
is  usually  done  by  means  of  attachment  to  a  skeleton  inside  the 
body.  In  man  they  may  be  of  two  kinds,  voluntary  (under  con- 
trol of  the  will)  and  involuntary. 


Diagrams  of  sections  of  cells,  greatly  magnified,  e,  flat  cell  (epithelium)  from 
mouth  ;  c,  columnar  epithelium  from  food  tube  ;  6,  bone-forming  cell  ;  I,  liver 
cell ;  m,  muscle  cell  ;  /,  fat  cell  ;  n,  nerve  cell. 

Epithelial  Cells.  —  Such  cells  cover  the  outside  of  a  body  or 
line  the  inside  of  the  cavities  in  the  body.  The  shape  of  such  cells 
varies  from  flat  plates  to  little  cubes  or  columns  depending  upon 
their  position  inside  or  outside  the  body.  Some  bear  ciha,  an 
adaptation.      Can  you  think  of  their  purpose  ? 

Connective  Tissue  Cells.  —  Such  cells  form  the  connection 
between  tissues  in  the  body.  They  are  characterized  by  possess- 
ing numerous  long  processes.  They  also  secrete,  as  do  many 
other  cells,  a  substance  like  jelly,  called  intercellular  substance. 
This  stands  in  the  same  relation  to  the  cells  as  does  mortar  to  the 
bricks  in  a  wall. 

Several  other  types  of  cells  might  be  mentioned,  as  blood  cells, 
cartilage  cells,  bone  cells,  and  nerve  cells.  A  glance  at  the  Figure 
shows  their  great  variety  of  shapes  and  sizes. 


206  THE   MET AZOA— DIVISION   OF   LABOR 

Functions  Common  to  All  Animals.  —  The  same  general  functions 
performed  by  a  single  cell  are  performed  by  a  many-celled  animal. 
But  in  the  Metazoa  the  various  functions  of  the  single  cell  are  taken 
up  by  the  organs.  In  a  complex  organism,  like  man,  the  organs 
and  the  functions  they  perform  may  be  briefly  given  as  follows  :  — 

(1)  The  organs  of  food  taking:  food  may  be  taken  in  by  indi- 
vidual cells,  as  those  lining  the  pores  of  the  sponge,  or  definite 
parts  of  a  food  tube  may  be  set  apart  for  this  purpose,  as  the  mouth 
and  parts  which  place  food  in  the  mouth. 

(2)  The  organs  of  digestion:  the  food  tube  and  collections  of 
cells  which  form  the  glands  connected  with  it.  The  enzymes  in  the 
fluids  secreted  by  the  latter  change  the  foods  from  a  solid  form 
(usually  insoluble)  to  that  of  a  fluid.  Such  fluid  may  then  pass  by 
osmosis  through  the  walls  of  the  food  tube  into  the  blood. 

(3)  The  organs  of  circulation :  the  tubes  through  which  the  blood, 
bearing  its  organic  foods  and  oxygen,  reaches  the  tissues  of  the  body. 
In  simple  forms  of  Metazoa,  as  the  sponge  and  hydra,  no  such 
organs  are  needed,  the  fluid  food  passing  from  cell  to  cell  by  osmosis. 

(4)  The  organs  of  respiration:  the  organs  in  which  the  blood 
receives  oxygen  and  gives  up  carbon  dioxide.  The  outer  layer  of 
the  body  serves  this  purpose  in  very  simple  animals ;  gills  or  lungs 
are  developed  in  more  complex  animals. 

(5)  The  organs  of  excretion :  such  as  the  kidneys  and  skin,  which 
pass  off  nitrogenous  and  other  waste  matters  from  the  body. 

(6)  The  organs  of  locomotion:  muscles  and  their  attachments 
and  connectives;  namely,  tendons,  ligaments,  and  bones. 

f  (7)  The  organs  of  nervous  control:  the  central  nervous  system, 
which  has  control  of  coordinated  movement.  This  consists  of 
scattered  cells  in  low  forms  of  life;  such  cells  are  collected  into 
groups  and  connected  with  each  other  in  higher  animals. 

(8)  The  sense  organs :  collections  of  cells  having  to  do  with  the 
reception  of  sight,  hearing,  smell,  taste,  and  touch. 

(9)  The  organs  of  reproduction:  the  sperm  and  egg-forming 
glands. 

Almost  all  animals  have  the  functions  mentioned  above.  In  most, 
the  various  organs  mentioned  are  more  or  less  developed,  although 
in  the  simpler  forms  of  animal  life  some  of  the  organs  mentioned 
above  are  either  very  poorly  developed  or  entirely  lacking. 


THE  METAZOA  — DIVISION   OF  LABOR 


207 


FORMS  OF   SIMPLE   METAZOANS.      SPONGES 


Sponges  may  be  placed,  according  to  the  kind  of  skeleton  they  possess, 
in  the  following  groups :  — 

(1)  The  limy  sponges,  in  which  the  skeleton  is  composed  of  spicules  of 
carbonate  of  lime.     Grantia  is  an  example. 

(2)  The  glassy  sponges.  Here  the  skeleton 
is  made  of  silica  or  glass.  Some  of  the  rarest 
and  most  beautiful  of  all  sponges  belong  in 
this  class.  The  Venus's  flower  basket  is  an 
example. 

(3)  The  horny  fiber  sponges.  These,  the 
sponges  of  commerce,  have  the  skeleton  com- 
posed of  tough  fibers  of  material  somewhat 
like  that  of  cow's  horn.  This  fiber  is  elastic 
and  has  the  power  to  absorb  water.  In  a 
living  state,  the  horny  fiber  sponge  is  a  dark- 
colored  fleshy  mass,  usually  found  attached 
to  rocks.  The  warm  waters  of  the  Mediter- 
ranean Sea  and  the  West  Indies  furnish  most 
of  our  sponges.  The  sponges  are  pulled  up 
from  their  resting  place  on  the  bottom,  either 
by  means  of  long-handled  rakes  operated  by 
men  in  boats,  or  are  secured  by  divers.  They 
are  then  spread  out  on  the  shore  in  the  sun, 
and  the  living  tissues  allowed  to  decay ;  then 

after  treatment  consisting  of  beating,  bleaching,  and  trimming,  the  bath 

sponge  is  ready  for  the  mar- 
ket. 

CCELENTERATES 


The  hydra  and  its  salt- 
water allies,  the  jellyfish, 
hydroids,  and  corals,  belong 
to  a  group  of  animals  known 
as  the  Ccelenterata.  The  word 
"  coelenterate  "  (cadom =hody 
cavity,  en/eron= food  tube) 
explains  the  structure  of  the 
group.  They  are  animals 
which  have  a  common  body 
cavity  and  food  tube,  the 
animal  in  its  simplest  form 
being  little  more  than  a 
bag. 


Venus's  flower  basket;  a 
Bponge  with  a  glassy  skele- 
ton. 


Medusa  {Gonionemus  murhachii),  showing  ten- 
tacles, mouth,  digestive  canals,  and  reproduc- 
tive bodies.  Photographed  from  the  model 
at  the  American  Museum  of  Natural  History. 


208         THE  MET AZOA— DIVISION  OF  LABOR 


Medusa.  —  Among  the  most  interesting  of  all  the  coelenterates  inhabit- 
ing the  salt  water  are  the  jellyfishes  or  medusae.  These  animals  vary 
greatly  in  size  from  a  tiny  umbrella-shaped  animal  little  larger  than  the 
head  of  a  pin  to  huge  jellyfish  several  feet  in 
diameter. 

Development.  —  Many  species  of  medusae 
pass  through  another  stage  of  life.  As  medusae 
they  reproduce  by  eggs  and  sperms,  that  is, 
sexually.  The  egg  of  the  medusa  segments, 
forming  ultimately  a  ball  of  cells  (the  blastrula) 
which  swims  around  by  means  of  cilia.  Ulti- 
mately the  little  animal  settles  down  on  one  end 
and  becomes  fixed  to  a  rock,  seaweed,  or  pile. 
The  free  end  becomes  indented  in  the  same 
manner  as  a  hollow  rubber  ball  may  be  pushed 
in  on  one  side.  This  indented  side  becomes  a 
mouth,  tentacles  develop  around  the  orifice,  and 
we  have  an  animal  that  looks  very  much  like 
the  hydra.  This  animal,  now  known  as  a  hy- 
droid  polyp,  buds  rapidly  and  soon  forms  a 
colony  of  little  polyps,  each  of  which  is  con- 
nected with  its  neighbor  by  a  hollow  food  tube. 
The  hydroid  polyp  differs  from  its  fresh-water 
cousin,  the  hydra,  by  usually  possessing  a  tough 
covering  which  is  not  alive. 

Alternation  of  Generations  in  Coelenterates. 
—  The  lives  of  a  hydroid  and  a  medusa  are  seen  thus  to  be  intimately 
connected  with  each  other.     A  hydroid  colony  produces  new  polyps  by 
budding.     This  we   know  is  an 
asexual  method  of  reproduction. 
There   come   from    this    hydroid 
colony,  however,  little  buds  which 
give  rise  to  medusae.     These  me- 
dusae produce  eggs  and  sperms. 
Their  reproduction  is  sexual,  as 
was  the  reproduction  by  means  of 
eggs  and  sperms  from  the  prothal- 
lus  of  the  fern.     So  we  have  in 
animals,  as  well  as  in  plants,  an 
alternation  of  generations. 

Sea  Anemone.  —  Those  who 
have  visited  our  New  England 
coast  are  familiar  with  another 
coelenterate  called  the  sea  anem- 
one.    This  animal  gets  its  name 


A  hydroid  colony  of  six 
polyps  :  /,  feeding  polyp  ; 
r,  reproductive  polyp ;  m, 
a  medusa ;  y,  young  polyp. 


Sea  anemone.  About  one  half  natural  size. 
The  right-hand  specimen  is  expanded. 
Note  the  mouth  surrounded  by  the  ten- 
tacles. The  left-hand  specimen  is  con- 
tracted. From  model  at  the  American 
Museum  of  Natural  History. 


THE   MET AZOA  — DIVISION   OF   LABOR 


209 


A  branching  nmdreporic  coral. 


because,  when  expanded,  it  looks  like  a  beautiful  flower  of  a  golden  yellow 
or  red  color.  The  body  of  the  sea  anemone  is  like  the  hydra,  a  column 
attached  at  one  end.  The  free  end  is  provided  with  a  mouth  surrounded 
with  a  great  number  of  tentacles.  These,  when  expanded,  look  like  the 
petals  of  a  flower.  The  sea 
anemone  is  a  very  voracious 
flower,  for  by  means  of  the  bat- 
teries of  stinging  cells  in  its  ten- 
tacles it  is  able  to  catch  and 
devour  fishes  and  other  animals 
almost  as  large  as  itself.  When 
disturbed  or  irritated,  the  ani- 
mal contracts  into  a  slimy  ball, 
making  it  difficult  to  dislodge 
from  its  attachment. 

Although  the  sea  anemone  is 
like  a  large  hydra  in  appearance, 
its  interior  is  different.  Th(> 
hollow  digestive  cavity  contains 
a  number  of  partitions  more  or 
less  complete,  which  run  from 

the  outer  wall  toward  the  middle  of  the  cavity.  These  partitions,  known 
as  mesenteries,  are  found  in  pairs.  Part  of  the  cavity,  as  in  the  hydra, 
is  g^iven  up  to  digesting  the  food.  Food  is  killed  by  means  of  stinging 
cells  found  in  the  long  threadlike  tentacles. 

Coral.  —  If  a  i^ioce  of  madreporic  coral  is  examined  with  a  hand  lens,  a 
number  of  little  depressions  will  be  seen  in  the 
limy  surface,  each  of  which  has  tiny  partitions 
within  it. 

These  cuplike  depressions  were  once  occu- 
pied by  the  coral  animals  or  polyps,  each  in  its 
own  cup.  The  mesenteries  of  the  coral  polyp 
are  paired  and  hollow  on  the  under  surface. 
The  partitions  seen  in  the  coral  cups  lie  be- 
tween the  pairs  of  mesenteries,  and  are  formed 
by  them  when  the  animal  is  alive.  Sea  water 
has  a  considerable  amount  of  lime  in  its 
composition.  This  lime  (calcium  carbonate)  is 
taken  from  the  water  by  certain  of  the  cells  of 
the  coral  polyp  and  deposited  around  the  base 
of  the  animal  and  between  the  mesenteries, 
thus  giving  the  appearance  just  seen  in  the 
cups  of  the  coral  branch. 
Asexual  Reproduction.  —  These  polyps  reproduce  by  budding,  and 
when  alive  cover  the  whole  coral  branch  with  a  continuous  living  mass  of 


A  single  coral  cup,  showing 
the  walls  of  lime  built  by 
the  mesenteries.  From 
a  photograph  loaned  by 
the  American  Museum 
of  Natural  History. 


HUNT.  ES.  BIO. 


14 


210  THE  METAZOA  — DIVISION   OF   LABOR 

polyps,  each  connected  with  its  neighbor.  In  this  way  great  masses  of 
coral  are  formed.  Coral,  in  a  living  state,  is  alive  only  on  the  surface, 
the  polyps  building  outward  on  the  skeleton  formed  by  their  predecessors. 

Economic  Importance  of  Corals.  —  Only  one  (astrangia)  of  a  great 
many  different  species  of  coral  lives  as  far  north  as  New  York.  In  tropical 
waters  they  are  very  abundant.  Coral  building  has  had  and  still  has  an 
immense  influence  on  the  formation  of  islands,  and  even  parts  of  conti- 
nents in  tropical  seas.  Not  only  are  many  of  the  West  Indian  islands 
composed  largely  of  coral,  but  also  Florida,  Australia,  and  the  islands  of 
the  southern  Pacific  are  almost  entirely  of  coral  formation. 

Coral  Reefs.  —  The  coral  polyp  can  live  only  in  clear  sea  water  of 
moderate  depth.  Fresh  water,  bearing  mud  or  other  impurities,  kills 
them  immediately.  Hence  coral  reefs  are  never  found  near  the  mouths 
of  large  fresh-water  rivers.  They  are  frequently  found  building  reefs 
close  to  the  shore.  In  such  cases  these  reefs  are  called  fringing  reefs. 
The  so-called  barrier  reefs  are  found  at  greater  distance  (sometimes  forty 
tb  fifty  miles)  from  the  shore.  An  example  is  the  Great  Barrier  Reef  of 
Australia.  The  typical  coral  island  is  called  an  atoll.  It  has  a  circular 
form  inclosing  a  part  of  the  sea  which  may  or  may  not  be  in  communica- 
tion with  the  ocean  outside  the  atoll.  The  atoll  was  perhaps  at  one  time 
a  reef  outside  a  small  island.  This  island  disappeared,  probably  by  the 
sinking  of  the  land.  The  polyps,  which  could  live  in  water  up  to  about 
one  hundred  and  fifty  feet,  continued  to  build  the  reef  until  it  arose  to 
the  surface  of  the  ocean.  As  the  polyps  could  not  exist  for  long  above  low- 
water  line,  the  animals  died  and  their  skeletons  became  disintegrated  by 
the  action  of  waves  and  air.  Later  birds  brought  a  few  seeds  there, 
perhaps  a  coconut  was  washed  ashore;  thus  plant  life  became  estab- 
lished in  the  atoll,  and  a  new  outpost  to  support  human  life  was  estab- 
lished. 

Classification  of  Ccelentbrates 

Class  I.  Hydrozoa.  Body  cavity  containing  no  mesenteries,  usually  alternation 
of  generation.     Examples :   Hydra,  hydroids. 

Class  II.  Scyphozoa.     Examples  :   large  jellyfishes. 

Class  III.  Actinozoa.  Mesenteries  present  in  body  cavity.  Examples :  sea  anem- 
ones and  corals. 

Class  IV.  Ctenophora. 

Reference  Books 
elementakt 

Sharpe,  A  Laboratory  Manual  for  the  Solution  of  Problems  in  Biology.    American 

Book  Company. 
Agassiz,  A  First  Lesson  in  Natural  History.     D.  C.  Heath  and  Company. 
Holder,  Half  Hours  with  the  I^ower  Animals.     American  Book  Company. 
Jordan,  Kellogg,  and  Heath,  Animal  Studies.     D.  Appleton  and  Company. 


THE  METAZOA— DIVISION  OF  LABOR  211 


ADVANCED 

Hertwig,  R.,  General  Principles  of  Zoology.     Henry  Holt  and  Company. 

Miner,  A  Guide  to  the  Sponge  Alcove.     Guide   Leaflet,  No.  23,  American  Museum 

of   Natural   History,    New   York. 
Parker,  Elementary  Biology.     The  Macmillan  Company. 
Parker  and  Haswell,  Textbook  of  Zoology.     The  Macmillan  Company. 
Sedgwick  and  Wilson,  General  Biology.     Henry  Holt  and  Company. 
Verworn,  General  Physiology.     The  Macmillan  Company. 


XVII.  THE    WORMS,   A  STUDY   OF    RELATIONS    TO    EN- 
VIRONMENT 

Trohlem  XXVII,  The  relation  of  the  earthworrvh  to  its  sur- 
roundings {optional).    {Laboratory  Manual,  Prob.  XXYII.) 

Effect  of  Surroundings  on  Plants.  —  Animals  as  well  as  plants 
are  influenced  very  greatly  by  their  surroundings  or  environment. 
We  have  seen  how  green  plants  behave  toward  the  various  factors 
of  their  environment ;  how  heat  and  moisture  start  germination  in 
a  seed;  how  the  roots  grow  toward  water;  how  gravity  influences 
the  root  and  the  stem,  pulling  the  root  downward  and  stimulating 
the  stem  to  grow  upward ;  how  the  stem  grows  toward  the  source  of 
light ;  and  how  the  leaves  put  their  flat  surfaces  so  as  to  get  as  much 
light  as  possible;  and  how  oxygen  is  necessary  for  life  to  go  on. 

It  is  quite  possible  to  show  that  the  factors  of  environment  act 
upon  animals  as  well  as  plants,  although  it  is  much  harder  to  ex- 
plain why  an  animal  does  a  certain  thing  at  a  certain  time. 

How  One-celled  Animals  respond  to  Stimuli.  —  We  have  seen 
that  the  single-celled  animals  respond  to  certain  stimuli  in  their 
surroundings.  The  presence  of  food  attracts  them;  when  they  run 
into  an  object,  they  respond  immediately  by  backing  away,  thus 
showing  that  they  have  a  sense  of  touch.  If  part  of  a  glass 
slide  containing  paramoecia  is  heated  slightly,  the  animals  will 
respond  to  the  increase  in  heat  by  moving  toward  the  cooler  end. 
Many  other  experiments  might  be  quoted  to  show  that  the  living 
matter  of  a  simple  animal  is  sensitive  to  its  surroundings. 

The  Earthworm  in  its  Relation  to  its  Surroundings.  —  The 
earthworm,  familiar  to  most  boys  as  bait,  shows  us  in  many  ways 
how  a  many-celled  animal  responds  to  stimuli.  Careful  observation 
of  the  body  of  a  living  earthworm  shows  us  that  its  long  tapering 
body  is  made  up  of  a  large  number  of  rings  or  segments.  The  num- 
ber of  these  segments  will  be  found  to  vary  in  worms  of  different 
size,  the  larger  worms  having  more  segments. 

If  the  two  ends  of  the  worm  be  touched  Ughtly  with  a  small  stick 

212 


THE    WORMS  213 

or  straw,  one  end  will  be  found  to  respond  much  more  readily  to 
touch  than  the  other  end.  The  more  sensitive  end  is  the  front 
or  anterior  end,  the  other  end  being  the  posterior  end.  Jar  the 
dish  in  which  the  worm  is  crawling;  it  will  immediately  respond 
by  contracting  its  body. 

Living  earthworms  tend  to  collect  along  the  sides  of  a  dish  or  in 
the  corners.  This  seems  to  be  due  to  an  instinct  which  leads  them 
to  inhabit  holes  in  the  ground. 

An  earthworm  placed  half  in  and  half  out  of  a  darkened  box  soon 


"X/ 


Au  earthworm  crawling  over  a  smooth  surface. 

responds  by  crawling  into  the  darkened  part  and  remaining  there. 
There  are  no  eyes  visible.  A  careful  study  of  the  worm  with  the 
microscope,  however,  has  revealed  the  fact  that  scattered  through 
the  skin,  particularly  of  the  anterior  segments,  are  many  little  struc- 
tures which  not  only  enable  the  animal  to  distinguish  between 
light  and  darkness,  but  also  light  of  low  and  high  intensity,  as  well 
as  the  direction  from  which  it  comes.  A  worm  has  no  ears  or 
special  organs  of  feeling.  We  know,  however,  that  although  a 
worm  responds  to  vibrations  of  low  intensity,  the  sense  of  touch  is 
well  developed  in  all  parts  of  the  body. 

It  also  responds  to  the  presence  of  food,  as  can  be  proved  if 
bits  of  lettuce  or  cabbage  leaf  are  left  overnight  in  a  dish  of 
earth  where  worms  are  kept. 

Locomotion  of  an  Earthworm.  —  If  we  measure  an  earthworm 
when  it  is  extended  and  compare  with  the  same  worm  contracted, 
we  note  a  difference  in  length.  This  is  accounted  for  when  we 
understand  the  method  of  locomotion.  Under  the  skin  are  two 
sets  of  muscles,  an  outer  set  which  passes  in  a  circular  direction 


214 


THE  WORMS 


around  the  body,  and  an  inner  set  which  runs  the  length  of  the 
body.  The  body  is  lengthened  by  the  contraction  of  the  cir- 
cular muscles.      How  might  the  body  be  shortened  ? 

The  under  surface  of  the  worm  is  provided 
with  four  double  rows  of  tiny  bristles  called 
setae,  every  segment  except  the  first  three  and 
the  last  being  provided  with  setae.  Each  seta 
has  attached  to  it  small  muscles,  which  turn 
the  seta  so  it  may  point  in  the  opposite  direc- 
tion from  which  the  worm  is  moving.  If  you 
watch  a  specimen  carefully,  you  will  see  that 
locomotion  is  accomplished  by  the  thrusting 
forward  of  the  anterior  end;  then  a  wave  of 
muscular  contraction  passes  down  the  body,  thus  shortening  the 
body  by  drawing  up  the  posterior  end.  The  setae  at  the  anterior 
end  serve  as  anchors  which  prevent  the  body  from  slipping  back- 
ward as  the  posterior  end  is  drawn  up. 

How  the  Worm  digs  Holes.  —  A  feeding  worm  will  show  the  proboscis, 
an  extension  of  the  upper  lip  which  is  used  to  push  food  into  the  mouth. 


Diagram  to  show  how 
movement  of  a  seta 
is  accomplished; 
M,  muscles;  S, 
seta ;  W,  body  wall. 
(After  Sedgwick 
and  Wilson.) 


Forepart  of  an  earthworm  with  the  left  body  wall  removed  to  show  the  body  cavity 
and  food  tube  within  it:  m,  mouth  ;  p,  pharynx,  c,  g,  i,  food  tube. 

The  earthworm  is  not  provided  with  hard  jaws  or  teeth.  Yet  it  literally 
eats  its  way  through  the  hardest  soil.  Inside  the  mouth  opening  is  a  part  of 
the  food  tube  called  the  pharynx.  This  is  very  muscular  so  that  it  can  be 
extended  and  withdrawn  by  the  worm.  When  applied  to  the  surface  of 
the  soil,  which  is  first  moistened  by  the  worm,  it  acts  as  a  suction  pump 
and  draws  it  into  the  food  tube.  As  the  worms  take  organic  matter  out 
of  the  ground  as  food,  they  pass  the  earth  through  the  body  in  order  to 


THE    WORMS 


215 


Diagrammatic  cross  section  of  the  body  of  a  coe- 
lenterate,  and  that  of  a  worm. 


get  this  food.  The  earth  is  mixed  with  fluids  poured  out  from  glands  in 
the  food  tube,  and  is  passed  out  of  the  body  and  deposited  on  the  surface 
of  the  ground,  in  the  form  of  little  piles  of  moist  earth.  These  are  familiar 
sights  on  all  lawns ;  they  are  called  worm  casts.  Charles  Darwin  cal- 
culated that  fifty-three  thousand  worms  may  be  found  in  an  acre  of  ground, 
that  ten  tons  of  soil  might  pass  through  their  bodies  in  a  single  year  and 
thus  be  brought  to  the  surface,  and  that  they  plow  more  soil  than  all  the 
farmers  put  together.  Earthworms,  in  spite  of  their  fondness  for  some 
garden  vegetables  and  young  roots,  do  much  good  by  breaking  up  the 
soil,  thus  allowing  water  and  oxygen  to  penetrate  to  the  roots  of  plants. 

Comparison  between  Hydra 
and  Worm.  —  The  digestive 
tract  of  the  worm  is  an  almost 
straight  tube  inside  of  another 
tube.  The  latter  is  divided 
by  partitions  which  mark  the 
boundary  of  each  segment. 
The  outer  cavity  is  known  as 
the  body  cavity.  In  the  hydra 
no  distinction  existed  between 
the  body  cavity  and  digestive 
tract.  In  the  animals  higher  than  the  coelenterates  the  digestive  tract 
and  body  cavity  are  distinct.  Food  is  digested  within  the  food  tube,  is 
passed  through  the  walls  of  this  tube  into  the  body  cavity,  and  is  in  part 
carried  by  the  blood  to  various  parts  of  the  body.  No  gills  or  lungs 
are  present,  the  thin  skin  acting  as  an  organ  of  respiration.  But  the 
worm  is  unable  to  take  in  oxygen  unless  the  membranelike  skin  is  kept 
moist. 

Development.  —  Notice  in  some  worms  the  swollen  area  called  the 
girdle  (about  one  third  the  distance  from  the  anterior  end).  This  area 
periodically  forms  a  little  sac  in  which  the  eggs  of  the  worm  are  laid.  As 
it  passes  toward  the  anterior  end  of  the  worm,  it  receives  from  the  body 
openings  the  sperms  and  a  nutritive  fluid  in  which  the  eggs  live.  The 
fertilized  eggs  are  then  left  to  hatch.  The  capsules  may  be  found  in 
manure  heaps,  or  under  stones,  in  May  or  June ;  they  are  small  yellow- 
ish or  brown  bags  about  the  diameter  of  a  worm. 

Regeneration.  —  If  a  one-celled  animal  be  cut  into  two  pieces,  each 
piece,  if  it  contains  part  of  the  nucleus,  will  grow  into  a  whole  cell.  The 
hydra,  some  hydroids,  jellyfish,  and  flatworms,  if  injured,  may  grow 
again  parts  that  are  lost.  This  power  is  known  as  regeneration.  Earth- 
worms possess  to  a  large  degree  the  power  of  replacing  parts  lost  through 
accident  or  other  means.  The  anterior  end  may  form  a  new  posterior 
end,  while  the  posterior  end  must  be  cut  anterior  to  the  girdle  to  form 
a  new  anterior  end.  This  seems  to  be  in  part  due  to  the  greater  com- 
plexity of  the  organs  in  the  anterior  end. 


216 


THE   WORMS 


The  Sandworm.  —  Other  segmented  worms  are  familiar  to  some  of  us. 

The  sandworm,  used  for  bait  along  our  eastern  coast,  is  a  segmented  worm 
which  lives  between  tide  marks  in  sandy  locahties.  It  is 
plainly  segmented,  each  segment  bearing  a  pair  of  loco- 
motor organs  called  parapodia  (meaning  side  feet).  A 
part  of  each  parapodium  is  prolonged  into  a  triangular 
gill.  The  animal  has  a  distinct  head,  which  is  provided 
with  tentacles,  palps,  and  eye  spots.  The  mouth  has  a 
pair  of  hard  jaws  which  may  be  protruded.  In  this  way 
the  animal  seizes  and  draws  prey  into  its  mouth.  The 
sandworm  swims  near  the  surface  of  the  water,  the  body 
bending  in  graceful  undulations  as  the  parapodia,  like  little 
oars,  force  the  worm  forward.  They  spend  much  of  the 
time  in  tubes  in  the  sand,  which  are  constructed  in  part  of 
slime  excreted  from  the  body  of  the  worm. 

The  Leech.  —  The  common  leech  or  bloodsucker  is  a 
flattened  segmented  worm,  inhabiting  fresh-water  ponds 
and  rivers.  The  adult  is  provided  with  two  sucking  disks, 
by  means  of  which  it  fastens  itself  to  objects.  The  mouth 
is  on  the  lower  surface  close  to  the  anterior  disk.  Loco- 
motion is  accomplished  by  swimming  or  by  means  of  the 
suckers,  somewhat  after  the  manner  of  a  measuring  worm. 
They  feed  greedily  and  are  often  found  gorged  with 
blood,   which   they   suck    from    the  body  of  the  victim. 

The  sandworm     Discomfort,  but  no  danger,  attends  the  bite  of  the  blood- 
(nereis).         sucker,  so  dreaded  by  the  small  boy. 

Problem  XXVIII,    A  study   of  some   animal  associations, 
{Laboratory  Manual,  Proh.  XXVIII.) 


worms   are   unseg- 


Some  Worms  which  harm  Man.  —  Some 
mented ;  such  are  the  flatworms  and 
roundworms.  A  common  leaflike 
form  of  flatworm  may  be  found  cling- 
ing to  stones  in  our  fresh-water  ponds 
or  brooks.  Most  flatworms  are,  how- 
ever, parasites  on  other  animals;  that 
is,  they  obtain  food  and  shelter  from 
some  other  living  creature,  but  give 
them  no  benefits  in  return.  Parasit- 
ism is  one-sided,  the  host  giving 
everything,  the  parasite  receiving  everything.  Consequently,  the 
parasite   frequently  becomes  fastened  to  its  host  during  adult  life 


A  flatworm  ( Yungia  Aurantiaca), 
much  magnified.  From  model 
in  the  American  Museum  of 
Natural  History. 


THE    WORMS  217 

and  often  is  reduced  to  a  mere  bag  through  which  the  fluid  food 
prepared  by  its  host  is  absorbed.  Such  animals  as  have  lost 
power  to  move  about  freely,  or  are  otherwise  changed  by  their 
surroundings,  are  said  to  have  degenerated. 

Sometimes  a  complicated  life  history  has  arisen  from  their  para- 
sitic habits.  Such  is  seen  in  the  life  history  of  the  liver  fluke,  a 
flatworm  which  kills  sheep,  and  in  the  tapeworm. 

Cestodes  or  Tapeworms.  —  These  parasites  infest  man  and 
many  other  vertebrate  animals.  The  tapeworm  {Tcenia  solium) 
passes  through  two  stages  in  its  hfe  history,  the  first  within  a  pig, 
the  second  within  the  intestine  of  man.  The  eggs  of  the  worm 
are  taken  in  with  the  pig's  food.  The  worm  develops  within  the 
intestine  of  the  pig,  but  soon  makes  its  way  into  the  muscles.  If 
man  eats  pork  containing  these  worms,  he  may  become  a  host  for 
the  tapeworm.  Another  common  tapeworm  parasitic  on  man 
lives  part  of  its  life  as  an  embryo  within  the  muscles  of  cattle. 
The  adult  worm  consists  of  a  round  headlike  part  provided  with 
hooks,  by  means  of  which  it  fastens  itself  to  the  wall  of  the 
intestine.  This  head  now  buds  off  a  series  of  segmentlike  struc- 
tures, which  are  practically  bags  full  of  eggs.  These  structures, 
called  proglottids,  break  off  from  time  to  time,  thus  allowing  the 
eggs  to  escape.  The  proglottids  have  no  separate  digestive 
systems,  but  the  whole  body  surface,  bathed  in  digested  food, 
absorbs  it  and  is  thus  enabled  to  grow  rapidly. 

Roundworms.  —  Still  other  wormhke  creatures  called  round- 
worms are  of  importance  to  man.  Some,  as  the  vinegar  eel  found 
in  vinegar,  or  the  pinworms  parasitic  in  the  lower  intestine,  par- 
ticularly of  children,  do  little  or  no  harm.  The  pork  worm  or 
trichina,  however,  is  a  parasite  which  may  cause  serious  injury. 
It  passes  through  the  first  part  of  its  existence  as  a  parasite  in  a  pig 
or  other  vertebrate  (dog,  cat,  ox,  or  horse),  where  it  encysts  itself 
in  the  muscles  of  its  hosts.  In  the  case  of  pork,  if  the  meat  is  eaten 
in  an  uncooked  condition,  the  cyst  is  dissolved  off  by  the  action  of 
the  digestive  fluids,  and  the  living  trichina  becomes  free  in  the 
intestine  of  man.  Here  it  bores  its  way  through  the  intestine  walls 
and  enters  the  muscles,  causing  inflammation  there.  This  causes 
a  painful  and  often  fatal  disease  known  as  trichinosis. 

The  Hookworm.  —  The  discovery  by  Dr.  C.  W.  Stiles  of  the 


218 


THE  WORMS 


Bureau  of  Animal  Industry,  that  the  laziness  and  shiftlessness  of  the 
''  poor  whites  "  of  the  South  is  partly  due  to  a  parasite  called  the 
hookworm,  reads  like  a  fairy  tale. 

The  people,  largely  farmers,  become  infected  with  a  larval  stage 
of  the  hookworm,  which  develops  in  moist  earth.  It  enters  the  body 
usually  through  the  skin  of  the  feet,  for  children  and  adults  alike, 
in  certain  localities  where  the  disease  is  common,  go  barefoot  to 
a  considerable  extent. 

A  complicated  journey  from  the  skin  to  the  intestine  now  fol- 


A  family  of  poor  whites  in  North  Carolina.     All  infected  with  hookworm 


lows,  the  larvae  passing  through  the  veins  to  the  heart,  from  there 
to  the  lungs ;  here  they  bore  into  the  air  passages  and  eventually 
reach  the  intestine  by  way  of  the  windpipe.  One  result  of  the 
injury  of  the  lungs  is  that  many  thus  infected  are  subject  to  tuber- 
culosis. The  adult  worms,  once  in  the  food  tube,  fasten  themselves 
and  feed  upon  the  blood  of  their  host  by  puncturing  the  intestine  wall. 
The  loss  of  blood  from  this  cause  is  not  sufficient  to  account  for 
the  bloodlessness  of  the  person  infected,  but  it  has  been  discovered 
that  the  hookworm  pours  out  a  poison  into  the  wound  which  pre- 


THE  WORMS  219 

vents  the  blood  from  coagulating  (see  page  367)  rapidly;  hence  a 
considerable  loss  of  blood  occurs  from  the  wound  after  the  worm 
has  finished  its  meal  and  gone  to  another  part  of  the  intestine. 

The  cure  of  the  disease  is  very  easy;  thymol,  which  weakens  the 
hold  of  the  worm,  being  followed  by  Epsom  salts.  For  years  the 
entire  South  undoubtedly  has  been  retarded  in  its  development 
by  this  parasite,  and  hundreds  of  millions  of  dollars  and,  what 
is  more  vital,  thousands  of  lives,  have  been  needlessly  sacrificed. 

"  The  hookworm  is  not  a  bit  spectacular :  it  doesn't  get  itself  dis- 
cussed in  legislative  halls  or  furiously  debated  in  political  campaigns. 
Modest  and  unassuming,  it  does  not  aspire  to  such  dignity.  It  is  satis- 
fied simply  with  (1)  lowering  the  working  efficiency  and  the  pleasure  of 
living  in  something  like  two  hundred  thousand  persons  in  Georgia  and 
all  other  Southern  states  in  proportion ;  with  (2)  amassing  a  death  rate 
higher  than  tuberculosis,  pneumonia,  or  typhoid  fever;  with  (3)  stub- 
bornly and  quite  effectually  retarding  the  agricultural  and  industrial  de- 
velopment of  the  section ;  with  (4)  nullifying  the  benefit  of  thousands  of 
dollars  spent  upon  education;  with  (5)  costing  the  South,  in  the  course 
of  a  few  decades,  several  hundred  millions  of  dollars.  More  serious  and 
closer  at  hand  than  the  tariff;  more  costly,  threatening,  and  tangible 
than  the  Negro  problem ;  making  the  menace  of  the  boll  weevil  laughable 
in  comparison  —  it  is  preeminently  the  problem  of  the  South."  —  Atlanta 
Constitution. 

Parasitic  worms  are  of  vital  importance  to  mankind.  Not 
only  do  they  levy  a  tax  of  death  and  illness  on  man  himself,  but 
they  destroy  as  well  unestimated  millions  of  dollars'  worth  of  ani- 
mals. Of  the  2,000,000  persons  infected  with  hookworm,  500,000 
are  wage  earners  (and  this  is  a  small  estimate) ;  their  earnings  at 
$1.50  a  day  would  amount  to  about  $225,000,000  a  year.  If  their 
wage-earning  capacity  were  decreased  only  10  per  cent,  it  is  seen 
that  a  loss  of  over  $20,000,000  a  year  could  be  directly  attributed 
to  this  pest. 

Other  Parasitic  Worms.  —  Some  roundworm  parasites  live  in 
the  skin,  and  others  live  in  the  intestines  of  the  horse.  Still  others 
are  parasitic  in  fish  and  in  insects,  one  of  the  commonest  being 
the  hair  snake,  often  seen  in  country  brooks. 


220  THE  WORMS 


Classification  of  Segmented  Worms  (Annulata) 

Class  I.   Choetopoda  (bristle-footed).     Segmented  worms  having  setae. 

Subclass  I.   Polychoeta    (many    bristles).     Having  parapodia  and  usually  head 

and  gills.     Example  :  sandworm. 
Subclass  II.   Oligochceta    (few    bristles).     No    parapodia,    head,    or    gills.     Ex- 
ample :    earthworm. 
Class  II.   Discophora   (bearing  suckers).     No  bristles,  two  sucking  disks  present. 
Example :    leech. 

Platyhblminthes  (Flat worms) 

Body  flattened  in  dorso-ventral  direction. 

Class  I.    Turbellaria.     Small,  aquatic,  mostly  not  parasitic.     Example :  planarian 
worm. 

Class  II.   Trematoda.     Usually    parasitic    worms    which    have    complicated    life 
history.     Example :    liver  fluke  of  sheep. 

Class  III.   Cestoda.      Internal     parasites     having    two    hosts.      Example :     tape- 
worm. 

Nemathelminthes  (Roundworms) 

Threadlike  worms,  mostly  parasitic.     Examples:  vinegar  eel.  Trichina,  and  hook- 
worm. 

Reference  Books 

elementary 

Sharpe,   A   Laboratory  Manual  for  the  Solution  of  Problems  in  Biology.    American 

Book  Company. 
Davison,  Practical  Zoology,  pages  150-161.     American  Book  Company. 
Herrick,  Textbook  in  General  Zoology,  Chap.  IX.     American  Book  Company. 
Jordan,  Kellogg,  and  Heath,  Animal  Studies,  VI.     D.  Appleton  and  Company. 
Ritchie,  Primer  of  Sanitation.    World  Book  Company. 

ADVANCED 

Darwin,  Earthworms  and  Vegetable  Mold.     D.  Appleton  and  Company. 
Sedgwick  and  Wilson,  General  Biology.     Henry  Holt  and  Company. 


XVIII.  THE   CRAYFISH.    A   STUDY   OF   ADAPTATIONS 

Problem,  XXIX.  A  study  of  the  idea  of  adaptations  as  shou/n 
in  the  crayfish  {optional).    (Laborai^ory  Manual,  Prob.  XXIX.) 

(a)  Protection. 

(b)  Locomotion. 

(c)  Surroundings. 

(d)  Feeding. 

(e)  Breathing. 

Adaptations.  —  Plants  and  animals  are  in  a  continual  struggle 
to  hold  the  places  they  have  obtained  upon  the  earth.  Continually 
we  see  garden  plants  driven  out  or  killed  by  the  competing  weeds, 
simply  because  the  weeds  are  better  fitted  or  adapted  to  live  under 
the  conditions  which  exist  in  the  garden,  especially  if  it  is  unculti- 
vated. An  adaptation  in  a  plant  or  animal  is  some  structure,  habit, 
or  abihty  which  is  of  advantage  to  the  organism  in  its  battle  for 
life.  We  have  seen  many  examples  of  adaptations  in  plants,  — 
adaptations  in  flowers  for  securing  cross-pollination,  in  fruits  for 
seed-scattering,  in  young  plants  for  protection,  in  roots  for  water- 
securing  ;    the  Hst  is  endless. 

In  animals,  likewise,  the  successful  competitors  are  the  ones  with 
adaptations  to  fit  them  for  living  in  the  particular  environment  or 
surroundings  in  which  nature  has  put  them.  Examples  are  often 
seen  where  animals,  hke  sheep  or  goats,  which  have  a  woolly  cover- 
ing, when  introduced  by  man  into  a  warmer  country,  die  because 
the  outer  coat  is  too  warm.  An  adaptation  for  withstanding  cold 
becomes  harmful  to  the  animal  under  conditions  of  greater  heat. 

One  adaptation  which  we  have  already  noticed  in  animals  is 
always  protective.  This  is  resemblance  of  the  animal  to  the  sur- 
roundings in  which  it  fives.  Other  adaptations  aid  the  animal  in 
obtaining  and  digesting  food,  in  protecting  itself  or  its  young 
from  attack  by  enemies,  and  in  many  other  ways  aiding  the  animal 
to  battle  successfully  with  the  dangers  around  it. 

221 


222  THE  CRAYFISH 

The  Crayfish.  Adaptations  for  Protection.  —  An  animal  which  well 
illustrates  adaptation  for  life  in  the  water  is  the  fresh-water  crayfish 
or  the  salt-water  lobster,  both  members  of  a  large  group  of  animals  known 
as  crustaceans.  The  body  of  such  an  animal  is  seen  to  be  covered  more  or 
less  completely  with  a  hard  covering,  which  is  jointed  in  the  posterior  region. 
This  exoskeleton  (outside  skeleton)  is  composed  largely  of  lime,  as  may  be 
proved  by  testing  with  acid.  The  exoskeleton  fits  over  the  anterior  part 
of  the  animal,  forming  an  unjointed  carapace,  or  armor.  This  armor  is 
clearly  protective  and  is  thus  an  adaptation.  If  the  crayfish  is  watched 
in  a  balanced  aquarium,  the  colors,  too,  are  seen  to  blend  remarkably 
with  the  stones  and  water  weeds  of  the  bottom.  The  animal  is  protec- 
tively colored.     The  under  s'de  of  the  animal  is  seen  to  be  less  well  pro- 


m 

Ch. 

C.P 

---^^^^b. 

1 

4, 

i 

Crayfish:     A.,  antennae;    E.,  stalked   eye;    C.P.,   cephalothorax ;    Ab.,    abdomen; 
C.F.,  caudal  fin;   M.,  mouth;    Ch.,  chehpeds.     From  photograph. 

tected  than  the  upper,  and  the  joints  of  the  abdomen,  or  posterior  region, 
are  seen  to  extend  completely  around  the  body.  The  animal  is  thus  seen 
to  be  segmented,  the  abdomen  showing  this  plainly.  The  seven  segments 
in  the  abdomen  are  constant  for  every  crayfish. 

Locomotion.  —  Those  of  us  who  have  caught  crayfish  in  fresh-water 
streams  or  lakes  know  that  it  takes  skill  and  quickness.  They  dart 
backwards  through  the  water  with  great  rapidity,  or  they  may  move 
forward  by  crawling  on  the  bottom.  Examination  of  a  crayfish  shows  us 
five  pairs  of  walking  legs  attached  to  the  under  side  of  the  cephalothorax 
(head  +  thorax),  the  anterior  part  of  the  body.  These  legs  are  jointed, 
the  first  three  bearing  pinchers.  The  large  pincher  claw  is  used  partly  for 
food-catching,  and  for  locomotion  as  well.  Try  to  find  out,  in  a  hving 
specimen,  exactly  what  part  it  plays. 

Under  the  abdomen,  one  to  each  segment  except  the  last,  are  found 
jointed  appendages,  made  up  of  three  parts,  a  base  and  two  branches. 
These  are  called  smmmerets,  though  they  are  not  used  for  swimming. 
Now  look  at  the  broad  pair  of  appendages  that,  together  with  the  last 


THE  CRAYFISH 


223 


segment  of  the  abdomen,  form  a  finlike  apparatus,  the  caudal  fin.  The 
caudal  fin  is  composed  of  two  large  swimmerets  and  the  last  body  segment. 
Crayfish  normally  swim  very 
rapidly  by  means  of  a  sudden 
jerking  in  a  backward  direc- 
tion of  the  caudal  fin.  The 
abdomen  is  provided  with 
powerful  muscles  which  are 
attached  to  the  exoskeleton. 
It  is  by  these  muscles  that 
the  rapid  swimming  is  ac- 
complished. 

How  the  Crayfish  gets  in 
Touch  with  its  Surroundings. 
—  Several  other  appendages 
besides  those  used  for  loco- 
motion are  found.  Two  pairs 
of  *'  feelers,"  the  longer  pair 
called  the  antenncB,  the  shorter 
the  antennules  (little  anten- 
nse),  protrude  from  the  front 
of  the  body.  The  longer 
feelers  appear  to  be  used  as 
organs  of  touch.  Certain 
hairlike  structures  projecting 
from  the  antennae  have  to  do 
with  the  sense  of  smell.  The 
smaller   antennules   hold    at 

their  bases  little  sacs  called  "ears."     These  "ears"  have  largely  to  do 
with  the  function  of  balancing  rather  than  hearing. 

Just  above  the  antennules,  projecting  on  stalks,  are  the  eyes.  These 
eyes  are  made  up  of  many  small  structures  called  ommatidia,  each  of 
which  is  a  very  simple  eye.  A  collection  of  ommatidia  is  known  as  a 
compound  eye.  A  little  bit  of  the  outer  covering  of  the  eye,  mounted 
under  a  compound  microscope,  shows  these  eye  units  to  be  shaped  like 
tiny  rectangles  in  cross  section.  Such  an  eye  probably  does  not  have 
very  distinct  vision  at  a  distance.  A  cray^fish,  however,  easily  distinguishes 
moving  objects  and  prefers  darkness  to  light,  as  may  be  proved  by  experi- 
ment. 

Feeding.  —  If  it  is  possible  to  have  the  aquarium  holding  the  crayfish 
in  the  schoolroom,  the  method  of  feeding  may  be  watched.  The  pincher 
claws  (chelipeds)  are  used  to  hold  and  tear  food,  as  well  as  for  defense 
and  offense.  Living  food  is  obtained  with  the  aid  of  the  chelipeds.  P^ood 
is  shoved  by  the  chelipeds  toward  the  mouth;  it  is  assisted  there  by 
three  pairs  of  small  appendages  called  foot  jaws  (maxillipeds),  and  to  a 


Female  lobster,  showing  eggs  attached  to  the 
swimmerets.  From  photograph  loaned  by  the 
American  Museum  of  Natural  History. 


224 


THE  CRAYFISH 


slight  degree  by  two  still  smaller  paired  maxillce  just  under  the  maxil- 
lipeds.  Ultimately  the  food  reaches  the  hard  jaws  and,  after  being  ground 
between  them,  is  passed  down  to  the  stomach. 

Breathing.  —  The  mouth  parts  of  a  crayfish  resting  in  the  aquarium 
are  observed  to  be  constantly  in  motion,  despite  the  fact  that  no  food 
is  present.  If  a  crayfish  is  taken  out  of  the  water  and  held  with  the 
ventral  surface  upmost,  a  little  carmine  (dissolved  in  water)  may  be 
dropped  on  the  lower  surface  and  allowed  to  run  down  under  the  cara- 
pace. If  now  the  animal  is  held  in  water  in  the  same  position,  the  carmine 
will  reappear  just  beyond  from  both  sides  of  the  mouth,  seemingly  pro- 
pelled by  something  which  causes  it   to  emerge  in  little  puffs.     If  we 


Some  appendages  of  the  crayfish:  1,  the  jaw,  with  palp;  2,  first  maxilla  (second 
maxilla  not  shown) ;  3,  third  maxilliped ;  4.  second  maxilliped,  showing  baler ; 
J,  first  maxilliped,  showing  gill  attached ;  6,  walking  appendage,  showing  attach- 
ment of  gill ;  7,  swimmeret ;  8,  uropod. 


remove  the  maxillipeds  and  maxillae  from  a  dead  specimen,  we  find  a 
groove  leading  back  from  each  side  of  the  mouth  to  a  cavity  of  con- 
siderable size  on  each  side  of  the  body  under  the  carapace.  This  is  the 
gill  chamber.  It  contains  the  gills,  the  organs  which  take  oxygen  out 
of  the  water.  The  second  maxillae  are  prolonged  down  into  the  groove 
to  serve  as  bailers  or  scoops.  By  rapid  action  of  this  organ  a  current 
of  water  is  maintained  which  passes  over  the  gills. 

The  gills  are  outside  of  the  body,  although  protected  by  the  carapace. 
If  the  carapace  is  partly  removed  on  one  side,  they  will  be  found  looking 
somewhat  like  white  feathers.  The  blood  of  the  crayfish  passes  by  a 
series  of  vessels  into  the  long  axis  of  the  gill ;  in  this  organ  the  blood 
tubes  divide  into  very  minute  tubes,  the  walls  of  which  are  extremely 


THE  CRAYFISH  226 

delicate.  Oxygen,  dissolved  in  the  water,  passes  into  the  blood  by  os- 
mosis, during  which  process  the  blood  loses  some  carbon  dioxide.  The 
gills  are  kept  from  drying  by  being  placed  in  a  nearly  closed  chamber, 
which  is  further  adapted  to  its  function  by  means  of  the  row  of  tiny  hairs 
which  border  the  lower  edge  of  the  carapace.  Thus  crayfish  may  live  for 
long  periods  away  from  water. 

Circulation.  —  The  circulation  of  blood  in  the  crayfish  takes  place  in 
a  system  of  thin-walled,  flabby  vessels  which  are  open  in  places,  allowing 
the  blood  to  come  in  direct  contact  with  the  tissues  to  which  it  flows. 
The  heart  lies  on  the  dorsal  side  of  the  body,  inclosed  in  a  delicate  bag, 
into  which  all  the  blood  in  the  body  eventually  finds  its  way  during  its 
circulation. 


Crayfish  with  the  left  half  of  the  body  structures  removed  :  a,  intestines ;  6,  ventral 
artery ;  c,  brain ;  e,  heart ;  et,  gastric  teeth ;  i,  oviduct ;  /,  digestive  gland : 
m,  muscles ;  n,  green  gland  (kidney) ;  o,  ovary ;  p,  pyloric  stomach ;  r,  nerve  cords : 
8,  cardiac  stomach ;  st,  mouth ;  u,  telson ;  w,  openings  of  veins  into  the  peri- 
cardial sinus.     Natural  size.     (Davison,  ZoQlogy.) 

Digestion.  —  Food  which  is  not  ground  up  into  pieces  small  enough 
for  the  purpose  of  digestion  is  still  further  masticated  by  means  of  three 
teeth,  strong  projections,  one  placed  on  the  mid-line  and  two  on  the  side 
walls  of  the  stomach.  The  exoskeleton  of  the  crayfish  extends  down 
into  the  stomach,  thus  forming  the  gastric  mill  just  described. 

The  stomach  is  divided  into  anterior  and  posterior  parts  separated 
from  each  other  by  a  constriction.  The  posterior  part  is  lined  with  tiny 
projections  from  the  wall  which  make  it  act  as  a  strainer  for  the  food 
passing  through.  Thus  the  larger  particles  of  food  are  kept  in  the 
anterior  end  of  the  stomach.  Opening  into  the  posterior  end  of  the 
stomach  are  two  large  digestive  glands  which  further  prepare  the  food  for 
absorption  through  the  walls  of  the  intestine.  Once  in  the  blood,  the 
fluid  food  is  circulated  through  the  body  to  the  tissues  which  need  it. 

Nervous  System.  —  The  internal  nervous  system  of  a  crayfish  con- 
sists of  a  series  of  collections  of  nerve  cells  {ganglia)  connected  by  means 
of  a  double  line  of  nerves.  Posterior  to  the  gullet,  this  chain  of  ganglia  is 
found  on  the  ventral  side  of  the  body,  near  the  body  wall.     It   then  en- 

HUNT.  ES.  BIO.  — 15 


226 


THE  CRAYFISH 


circles  the  gullet  and  forms  a  brain  in  the  head  region,  the  latter  formed 
from  several  ganglia  which  have  grown  together.  From  each  of  the 
ganglia,  nerves  pass  off  to  the  sense  organs  and  into  the  muscles  of  the 
body.  These  nerve  fibers  are  of  two  sorts,  those  bearing  messages  from 
the  outside  of  the  body  to  the  central  nervous  system  (these  messages 
result  in  sensations),  and  those  which  take  outgoing  messages  from  the 
central  nervous  system  (motor  impulses),  which  result  in  muscular  move- 
ments. 

Development.  —  The  sexes  in  the  crayfish  are  distinct.  The  eggs  are 
fertihzed  by  the  sperm  cells  as  they  pass  to  the  outside  of  the  body  of  the 
female.  The  developing  eggs,  which  are  provided  with  a  considerable 
supply  of  food  material  called  yolk,  are  glued  fast  to  the  swimmerets  of 
the  mother,  and  there  develop  in  safety.  The  young,  when  they  first 
hatch,  remain  clinging  to  the  swimmerets  for  several  weeks. 

Excretion  of  Wastes.  —  On  the  basal  joint  of  the  antennae  are  found  two 
projections,  in  the  center  of  which  are  found  tiny  holes.  These  are  the  open- 
ings of  the  green  glands,  organs  which  have  the  function  of  the  elimination 
of  nitrogenous  waste  from  the  blood,  the  function  of  the  human  kidneys. 


North  American  lobster.  This 
specimen,  preserved  at  the 
U.S.  Fish  Commission  at 
Woods  Hole,  was  of  unusual 
size  and  weighed  over  twenty 
pounds.  Notice  the  chelipeds. 


The  North  American  Lobster.  —  In 

structure  it  is  almost  the  counterpart 
of  its  smaller  cousin,  the  crayfish.  Its 
geographical  range  is  a  strip  of  ocean 
bottom  along  our  coast,  estimated  to 
vary  from  thirty  to  fifty  miles  in  width. 
This  strip  extends  from  Labrador  on 
the  north  to  Delaware  on  the  south. 
The  lobster  is  highly  sensitive  to 
changes  in  temperature.  It  migrates 
from  deep  to  shallow  water,  or  vice 
versa,  according  to  the  temperature  of 
the  water,  which  in  winter  is  relatively 
warmer  in  deep  water  and  cooler  in 
shallows.  Sudden  changes  in  the  water 
of  a  given  locality  may  cause  them  to 
disappear  from  that  place.  The  more 
abundant  food  supply  near  the  shore 
also  aids  in  determining  the  habitat  of 
the  lobster.  Lobsters  do  not  appear 
to  migrate  north  and  south  along  the 
coast.    While   little   is   known    about 


THE  CRAYFISH 


227 


their  habits  on  the  ocean  bottom,  it  is  thought  that  they  construct 
burrows  somewhat  Hke  the  crayfish,  in  which  they  pass  part  of  the 
time.  As  they  have  the  color  of  the  bottom  and  as  they  pass  much 
of  their  time  among  the  weed-covered  rocks,  they  are  able  to  catch 
much  living  food,  even  active  fishes  falling  prey  to  their  formidable 
pinchers.  They  move  around  freely  at  night,  usually  remaining 
quiet  during  the  day,  especially  when  in  shallow  water.  They  eat 
some  dead  food ;  and  thus,  like  the  crayfish,  they  are  scavengers. 
Development.  —  The  female  lobsters  begin  to  lay  eggs  when 
about  seven  inches  in  length.  Lobsters  of  this  size  lay  in  the 
neighborhood  of  five  thousand  eggs;  this  number  is  increased  to 
about  ten  thousand  in  lobsters  of  moderate  size  (ten  inches  in 
length) ;  in  exceptionally  large  speci- 
mens as  many  as  one  hundred  thou- 
sand eggs  are  sometimes  laid.  The 
eggs  are  laid  every  alternate  year, 
usually  during  the  months  of  July 
and  August.  Eggs  laid  in  July  or 
August,  as  shown  by  observations 
made  along  the  coast  of  Massa- 
chusetts, hatch  the  following  May 
or  June.  The  eggs  are  provided 
with  a  large  supply  of  yolk  (food), 
the  development  of  the  young  ani- 
mal taking  place  at  the  expense  of 
this  food  material.  After  the  young 
escape  from  the  egg,  they  are  almost 
transparent  and  little  like  the  adult 
in  form.  During  this  period  of  their 
lives  the  mortality  is  very  great,  as 
they  are  the  prey  of  many  fish  and  other  free-swimming  animals. 
It  is  estimated  that  barely  one  in  five  thousand  survives  this 
period  of  peril.  At  this  time  they  grow  rapidly,  and  in  conse- 
quence are  obliged  to  shed  their  exoskeleton  (molt)  frequently. 
During  the  first  six  weeks  of  life,  when  they  swim  freely  at  the 
surface  of  the  water,  they  molt  from  five  to  six  times.  ^ 

^  Recent  economic  investigations  upon  the  care  of  the  young  developing  lobster 
show  that  animals  protected  during  the  first  few  months  of  free  existence  have 


Metamorphosis  of  a  shrimp :  a,  nau- 
plius  or  earliest  stage ;  b,  c,  d,  later 
larval  stages ;  e,  adult.  Note  that 
as  the  animal  grows  more  append- 
ages appear,  and  that  these  develop 
backward  from  the  anterior  end. 


228  THE  CRAYFISH 

Molting.  —  During  the  first  year  of  its  life  the  lobster  molts  from 
fourteen  to  seventeen  times.  During  this  period  it  attains  a  length 
of  from  two  to  three  inches.  Molting  is  accomphshed  in  the  follow- 
ing manner  :  The  carapace  is  raised  up  from  the  posterior  end  and 
the  body  then  withdrawn  through  the  opening  between  it  and  the 
abdomen.  The  most  wonderful  part  of  the  process  is  the  with- 
drawal of  the  flesh  of  the  large  claws  through  the  very  small  openings 
which  connect  the  Hmbs  with  the  body.  The  blood  is  first  with- 
drawn from  the  appendage ;  this  leaves  the  flesh  in  a  flabby  con- 
dition (a  state  similar  to  the  taproot  which  has  lost  water  by  osmosis) 
so  that  the  muscles  can  be  drawn  through  without  injury.  The 
lobster  also  molts  a  part  of  the  lining  of  the  digestive  tract  as  far 
as  the  posterior  portion  of  the  stomach.  Immediately  after  molt- 
ing the  lobster  is  in  a  helpless  condition,  and  is  more  or  less  at  the 
mercy  of  its  enemies  until  the  new  shell,  which  is  secreted  by  the 
skin,  has  grown. 

Economic  Importance.  —  The  lobster  is  highly  esteemed  as 
food,  and  is  rapidly  disappearing  from  our  coasts  as  the  result  of 
overfishing.  Between  twenty  million  and  thirty  million  are  yearly 
taken  on  the  North  Atlantic  coast.  This  means  a  value  at  present 
prices  of  about  $15,000,000.  Laws  have  been  enacted  in  New  York 
and  other  states  against  overfishing.  Egg-carrying  lobsters  must 
be  returned  to  the  water ;  all  smaller  than  six  to  ten  and  one  half 
inches  in  length  (the  law  varies  in  different  states)  must  be  put 
back;  other  restrictions  are  placed  upon  the  taking  of  the 
animals,  in  hope  of  saving  the  race  from  extinction.  Some  states 
now  hatch  and  care  for  the  young  for  a  period  of  time;  the 
United  States  Bureau  of  Fisheries  is  also  doing  much  good  work, 
in  hope  of  restocking  to  some  extent  the  now  almost  depleted 
waters. 

Shrimps.  —  Several  other  common  crustaceans  are  near  relatives  of 
the  crayfish.  Among  them  are  the  shrimps  and  prawns,  thin-shelled, 
active  crustaceans  common  along  our  eastern  coast.  In  spite  of  the  fact 
that  they  form  a  large  part  of  the  food  supply  of  many  marine  animals, 
especially  fishes,  they  do  not  appear  to  be  decreasing  in  numbers.     Be- 

a  far  better  chance  of  becoming  adults  than  those  left  to  grow  up  without  protec- 
tion. Later  in  life  they  sink  to  the  bottom,  and  because  of  their  protectively  colored 
shell  and  the  habit  of  hiding  under  rocks  and  in  burrows,  they  are  comparatively 
safe  from  the  attack  of  enemies. 


THE  CRAYFISH 


229 


sides  this  value  as  a  food,  they  are  also  used  by  man,  the  shrimp  fisheries 
in  tliis  country  aggregating  over  $1,000,000  yearly. 

The  Blue  Crab.  —  Another  edible  crustacean  of  considerable  economic 
importance  is  the  blue  crab.  Crabs  are  found  inhabiting  muddy  bot- 
toms ;  in  such  localities  they 
are  caught  in  great  numbers 
in  nets  or  traps  baited  with 
decaying  meat.  They  are, 
indeed,  among  our  most  valu- 
able sea  scavengers,  although 
they  are  carnivorous  hunters 
as  well.  The  body  of  the 
crab  is  short  and  broad,  be- 
ing flattened  dorso-ventrally. 
The  abdomen  is  much  re- 
duced in  size.  Usually  it  is 
carried  close  to  the  under 
surface  of  the  cephalothorax ; 

in  the  female  the  eggs  are  carried  under  its  ventral  surface,  fastened  to 
the  rudimentary  swimmerets  in  the  position  which  is  usual  for  other 
crustaceans.  The  young  crabs  differ  considerably  in  form  from  the  adult. 
They  undergo  a  complete  metamorphosis  (change  of  form),  and  their 
method  of  life  differs  from  the  adult.  Immediately  after  molting,  crabs 
are  greatly  desired  by  man  as  an  article  of  food.  They  are  then  known 
as  "  shedders,"  or  soft-shelled  crabs. 

Other  Crabs.  —  Other  crabs  seen  along  the  New  York  coast  are  the 
prettily  colored  lady  crabs,  often  seen  running  along  our  sandy  beaches  at 
low  tide ;  the  fiddler  crabs,  interesting 
because    of   their   burrows  and  gre- 
garious   habits;    and    perhaps   most 
interesting  of   all,  the  hermit  crabs. 


The  edible  blue  oral).     From  photograph  loaned 
by  the  American  Museum  of  Natural  History. 


The  fiddler  crab.  From  photograph 
loaned  by  the  American  Museum  of 
Natural  History. 


Hermit  crab,  about  twice  natural  size. 
From  photograph  loaned  by  the  Amer- 
ican Museum  of  Natural  History. 


The  hermit  crabs  use  the  shells  of  snails  as  homes.     The  abdomen  is  soft, 
and  unprotected  by  a  limy  exoskeleton,  and  has  adapted  itself  to  its  con- 


230 


THE  CRAYFISH 


ditions  by  curling  around  in  the  spiral  snail  shell,  so  that  it  has  become 
asymmetrical.  These  tiny  crabs  are  great  fighters  and  wage  frequent 
duels  with  each  other  for  possession  of  the  more  desirable  shells.  They 
exchange  their  borrowed  shells  for  l^irger  ones  as  growth  forces  them  from 
their  first  homes. 

The  habits  of  these  animals,  and  those  of  the  fiddler  crabs,  might  be 
studied  with  profit  by  some  careful  boy  or  girl  who  spends  a  summer 
at  the  seashore  and  has  the  time  and  inclination  to  devote  to  the  work. 
Of  especial  interest  would  be  a  study  of  the  food  and  feeding  habits  of 
the  fiddler  crabs. 

A  deep-water  crab  often  seen  along  Long  Island  Sound  is  the  spider 
crab,  or  "  sea  spider,"  as  it  is  incorrectly  called  by  fishermen.     This 

animal,  with  its  long  spider- 
like legs,  is  neither  an  active 
runner  nor  swimmer;  it  is, 
however,  colored  like  the  dark 
mud  and  stones  over  which  it 
crawls  ;  thus  it  is  enabled  to 
approach  its  prey  without  be- 
ing noticed.  The  resemblance 
to  the  bottom  is  further 
heightened  by  the  rough  body 
covering,  which  gives  a  hold 
for  seaweeds  and  sometimes 
sessile  animals,  as  barnacles, 
hydroids,  or  sea  anemones, 
to  fasten  themselves. 

A  spider  crab  from  the  Sea 
of  Japan  is  said  to  be  the 
largest  crustacean  in  the 
world,  specimens  measuring 
eighteen  feet  from  tip  to  tip 
of  the  first  pair  of  legs  having 
been  found. 


Giant  spider  crab  from  Japan.  From  photograph 
loaned  by  the  American  Museum  of  Natural 
History. 


Symbiosis.  —  Certain  of  the  spider  crabs,  as  well  as  some  of  the 
larger  deep-water  hermit  crabs,  have  come  to  live  in  a  relation  of 
mutual  helpfulness  with  hydroids,  sponges,  and  sea  anemones. 
These  animals  attach  themselves  to  the  shell  of  the  crab  and  are 
carried  around  by  it,  thus  receiving  a  constant  change  of  position 
and  a  supply  of  food.  What  they  do  for  the  crab  in  return  is  not 
so  evident,  although  one  large  Chinese  hermit  regularly  plants  a 
sea  anemone  on  its  big  claw ;  when  forced  to  retreat  into  its  shell, 
the  entrance  is  thus  effectually  blocked  by  the  anemone.    The 


THE   CRAYFISH 


231 


living  of  animals  in  a  mutually  helpful  relation  has  been  referred 
to  as  symbiosis.  Of  this  we  have  already  had  some  examples  in 
plants  as  well  as  among  animals.     (See  page  187.) 

Habitat.  —  Most  crustaceans  Site  adapted  to  live  in  the  water ; 
a  few  forms,  however,  are  found  hving  on  land.  Such  are  the 
wood  lice,  the  pill  bugs,  which  have  the  habit  of  rolling  up  into  a 
ball  to  escape  attack  of  enemies,  the  beach  fleas,  and  others.  The 
coconut  crab  of  the  tropics  climbs  trees  in  search  of  food,  return- 
ing to  the  water  at  intervals  to  moisten  the  gills. 

Characters  of  Cra3rfish  and  its  Allies.  —  Our  study  of  cray^sh 
shows  us  that  animals  belonging  to  the  same  group  as  itself  have 
several  well-marked  characteristics.  The  most  important  are  the 
presence  of  a  segmented  Umy  exoskeleton,  gills,  jointed  appendages, 
usually  a  pair  to  each  segment  of  the  body  (except  the  last),  stalked 
compound  eyes,  and  the  fact  that  they  pass  through  a  metamor' 
phosis  or  change  of  form  before  they  reach  the  adult  state. 

We  find  that  the  Crustacea  fall  naturally  into  two  classes, 
those  in  which  the  number  of  pairs  of  appendages  varies,  and 
those  in  which  the  number  is  fixed  at  nineteen.  In  this  latter  class 
are  placed  the  crayfish,  lobster,  blue  crab,  shrimp,  and  most  of 
our  common  crustaceans. 

Entomostraca.  —  Another  sub- 
class of  crustaceans,  in  which  the 
number  of  appendages  varies,  is 
the  group  Entomostraca.  They  are 
mostly  small  animals,  some  species 
existing  in  countless  numbers.  One 
of  the  largest  Entomostracans  in- 
habiting fresh  water  is  the  fairy 
shrimp  (branchippus)  found  ap- 
pearing in  early  spring  in  fresh- 
water ponds,  a  little  translucent 
swimming  animal  from  one  half  to 
three  fourths  of  an  inch  in  length. 
Another  fresh-water  form  often 
seen  in  aquaria  is  the  water  flea 
(daphnia).  From  the  economic 
standpoint,  probably  the  most  un-  Cyclops  (note  the  single  eye-spot).  This 
portant  crustaceans  that  we  shall  is  a  very  common  copepod  and  is  mag- 
study  are  the  copepods.    These  tiny       nified  about  forty  times,    e,  egg  masses. 


232  THE   CRAYFISH 

animals  are  barely  visible  to  the  naked  eye.  They  are  found  in  almost 
every  part  of  the  world,  from  the  arctic  seas  to  those  of  the  tropics,  and 
in  fresh  as  well  as  salt  water.  They  are  so  numerous  that  the  sea  in  places 
is  colored  by  their  bodies.  So  prolific  are  they  that  it  is  estimated  that 
one  copepod  may  produce  in  a  single  year  four  billion  five  hundred  million 
offspring.  These  animals  form  a  large  part  of  the  food  supply  of  many 
of  our  most  important  food  fishes  as  well  as  the  food  of  many  other  aquatic 
animals.  The  whale,  for  example,  subsists  largely  on  this  kind  of  food. 
They  are,  then,  in  an  indirect  way,  of  immense  economic  value. 

Degenerate  Crustaceans.  —  One  of  the  most  interesting  forms  to  a 
zoologist  is  the  goose  barnacle.  This  crustacean,  like  all  others  of  the 
group,  is  free-swimming  during  its  early  life.  Later,  however,  after  passing 
through  several  changes  in  form  during  its  development,  the  barnacle 
settles  down  on  a  rock  or  some  floating  object,  fastens  itself  along  the 
dorsal  surface,  and  remains  fastened  during  the  rest  of  its  life.  Food 
comes  to  it  in  a  current  of  water,  which  is  set  in  motion  by  the  rhyth- 
mical beating  of  the  appendages.  Thus  food  particles  are  carried  along 
the  ventral  side  of  the  body  to  the  mouth.  Such  animals,  having  lost 
the  power  of  locomotion,  are  said  to  be  degenerate. 

Parasitic  Crustaceans.  —  Other  crustaceans  have  become  even  more 
helpless  and  have  come  to  take  their  living  from  other  animals.  In  some 
cases  they  become  simply  a  bag  for  absorbing  nourishment  from  the  host 
on  which  they  are  fastened.  Such  is  the  sacculina,  a  degenerate  crusta- 
cean that  lives  attached  to  the  body  of  the  crab.  Others  attach  them- 
selves to  fishes  and  are  known  to  fishermen  as  fish  lice. 

Reference  Books 

elementary 

Sharpe,  A  Laboratory  Manual  for  the  Solution  of  Problems  in  Biology.    American 

Book  Company. 
Burnet,  School  Zoology,  pages  67-73.     American  Book  Company. 
Davison,  Practical  Zoology,  pages  133-141.     American  Book  Company. 
Herrick,  Textbook  in  General  Zoology,  Chap.  XIII.     American  Book  Company. 
Jordan  and  Kellogg,  Animal  Life,  Chap.  VIII.     D.  Appleton  and  Company. 
Jordan,  Kellogg,  and  Heath,  Animal  Studies,  Chap.  IX.     D.  Appleton  and  Com- 
pany. 

ADVANCED 

Herrick,  The  American  Lobster,  Report  of  U.S.  Fish  Commission,  1895. 

Huxley,  The  Crayfish.     D.  Appleton  and  Company. 

Mead,  Reports  of  the  R.I.  Inland  Fisheries  Commission. 

Parker,  Elementary  Biology.     The  Macmillan  Company. 

Parker  and  Haswell,  Textbook  of  Zoology.     The  Macmillan  Company. 


XIX.  THE  INSECTS 

Problem  XXX,  A  study  of  some  anirndl  likenesses  and  dif- 
ferences, and  the  classification  of  insects  {optional).  {Laboratory 
Manual,  Prob.  XXX.) 

{a)  Grasshopper— a  straight-winged  insect. 

(b)  Butterfly  or  moth— a  scale-winged  insect, 

(c)  Tlie  typlwid  fly  —  a  two-winged  insect, 

(d)  A  beetle— a  sheath-winged  insect, 
ie)  A  bug — a  ha2f -winged  insect. 

(/)  The  dragon  fly — a  nerve-winged  insect, 
ig)  The  bee  —  a  membrane-winged  insect. 
(Jv)  Summ^ary  of  differences  between  orders, 
(i)  Making  a  logical  definition. 

Insects  the  Winners  in  Life's  Race.  —  We  are  all  familiar  with 
common  examples  of  insect  life.  Bees  and  butterflies  we  have 
already  studied  in  connection  with  their  work  in  the  cross-pollina- 
tion of  flowers.  Mosquitoes  and  flies  all  too  often  come  to  our 
notice  as  pests ;  the  common  household  insects  sometimes  annoy 
us,  while  we  often  hear  and  see  in  a  small  way  the  harm  done  by 
insects  in  the  field  and  garden.  Insects  are  a  successful  group. 
They  outnumber  all  the  other  species  of  animals  on  the  face  of  the 
earth.  They  hold  their  own  in  the  air,  in  the  water,  and  on  land. 
Fitted  in  many  ways  to  lead  the  successful  life,  they  have  become 
winners  in  life's  race. 

We  have  already,  from  our  study  of  a  bee,  formed  some  idea  of 
what  an  insect  is.  But  it  would  be  unfair  to  expect  to  know  all 
insects  from  our  slight  knowledge  of  one  form.  Our  object  in  the 
study  of  this  chapter  will  be  to  get  some  first-hand  knowledge 
of  some  common  insects  so  that  we  may  classify  them  and 
distinguish  one  from  another.  This  great  group,  containing  more 
than  half  of  the  known  representatives  of  animal  life  on  the  earth, 
is  made  up  of  a  number  of  groups  called  orders.  The  insects 
contained  in  these  orders  have  certain  characters  of  structure  and 

23a 


234 


THE  INSECTS 


life  history  in  common,  yet  each  differs  somewhat  from  the  other 
orders.  The  characters  which  all  the  groups  contain  in  common 
give  us  a  working  definition  of  an  insect. 

One  of  the  most  common  insects  in  the  United  States  is  the  locust 
or  grasshopper,  as  it  is  commonly  called.  The  study  of  a  living 
specimen  (or  if  it  cannot  be  obtained,  a  dead  locust)  will,  better 
than  any  other  insect,  give  us  insight  into  the  structure  and  life 
processes  of  this  great  group. 

The  Locust  (Red-legged  Grasshopper).  —  The  segmented  body 
is  divided  into  a  head,  sl  middle  portion  (the  thorax),  and  a  pos- 
terior part,  the  abdomen. 
The  legs,  six  in  number, 
and  two  pairs  of  wings 
are  attached  to  the  thorax. 
The  animal  lives  a  rather 
active  life  in  the  fields, 
the  hind  pair  of  legs  be- 
ing adapted  by  shape, 
position,  and  in  structure 
for  leaping.  Careful  ex- 
amination of  the  foot  of 
the  animal  shows  a  num- 
ber of  tiny  hooks  and  pads,  by  means  of  which  the  foot  is  fitted 
for  chnging  to  the  swaying  grass  stalks. 

Wings.  —  The  membranelike  wings,  when  spread  out,  show 
differences  in  structure.  Notice  the  many  veins.  The  outer  pair, 
strong  and  narrower  than  the  inner  pair,  serve  to  protect  the  inner 
wings,  used  for  flying,  which  when  at  rest  fold  up  like  a  fan.  The 
animal,  when  in  its  natural  habitat,  is  nearly  the  color  of  the  grass 
on  which  it  lives.  The  tough  exoskeleton  covering  the  body  is 
formed  largely  of  chitin,  a  substance  somewhat  Hke  that  which 
forms  the  horns  of  a  cow. 

Thorax. — Three  segments  form  the  thorax,  each  bearing  a  pair  of 
jointed  legs,  the  two  posterior  segments  bearing  wings  also. 

The  Abdomen.  —  The  segmented  abdomen  does  not  bear  ap- 
pendages, but  at  the  posterior  end  of  the  abdomen  of  the  female 
are  found  paired  movable  pieces  which  together  form  the  egg  layer 
or  ovipositor.    The  male  grasshopper  has  a  rounded  abdomen. 


Locust  (lubber  grasshopper)  :  AB,  abdomen; 
ANT,  antennae;  E,  eye;  M,  mouth;  P,  pads 
on  feet;  T,  thorax;  OV,  ovipositor. 


THE    INSECTS 


235 


Breathing  Organs.  —  Observation  of  the  abdomen  of  a  Hving 
grasshopper  shows  a  frequent  movement  of  the  abdomen.  Along 
the  side  of  the  abdomen  in  eight  of  the  segments  (in  the  red-legged 
grasshopper)  are  found  tiny  openings  called  spiracles.  A  large 
spiracle  may  easily  be  found  in  the  middle  segment  of  the  thorax. 
These  spiracles  open  into  little  tubes  called  trachece.  The  tracheae 
carry  air  to  all  parts  of  the  body.  By  the  movements  of  the  abdo- 
men just  noted,  air  is  drawn  into  and  forced  out  of  the  tracheae. 
The  tracheae  divide  and 
subdivide  like  branches  of 
a  tree,  so  that  all  the  body 
cavity  is  reached  by  their 
fine  endings.  Some  even 
pass  outward  into  the  veins 
of  the  wings.  Each  of  these 
tubes  contains  air.  The 
blood  of  an  insect  does  not 
circulate  through  a  system 
of  closed  blood  tubes  as  in 
man,  but  instead  it  more  or 
less    completely    fills    that 

part  of  the  body  cavity  which  is  not  filled  with  other  organs. 
Oxygen  is  thus  brought  in  contact  with  the  blood  by  means  of 
the  tracheae. 

Muscular  Activity.  —  Insects  have  the  most  powerful  muscles  of 
any  animals  of  their  size.  Relatively,  an  enormous  amount  of 
energy  is  released  during  the  jumping  or  flying  of  a  grasshopper. 
The  tracheae  pass  directly  into  the  muscles  and  other  tissues. 
Here  oxygen  is  passed  into  the  tissues,  and  oxidation  takes  place 
when  work  is  done. 

Food-Taking  and  Blood-Making.  —  The  grasshopper  is  provided 
with  two  pairs  of  jaws,  a  forklike  ventral-lying  pair,  the  maxillce,  and 
a  pair  of  hard  cutting  jaws,  the  mandibles.  These  parts  are  covered  when 
not  in  use  by  two  flaps,  the  upper  and  lower  hps.  The  plant  food  taken  by  the 
grasshopper  is  held  in  place  in  the  mouth  by  means  of  the  little  jaws,  or  the 
maxillae,  while  it  is  cut  into  small  pieces  by  the  mandibles.  Just  behind 
the  mouth  is  a  large  crop  into  which  empty  the  contents  of  the  salivary 
glands.  It  is  this  fluid  mixed  with  digested  food  that  we  call  the  "  grass- 
hopper's molasses."     After  the  food  is  digested  by   the  action  of  the 


Cross  section  through  the  body  of  an  insect: 
a,  food  tube;  h,  heart;  n,  nerve  cord;  t, 
tracheae  opening  at  t  by  spiracle. 


236 


THE  INSECTS 


saliva  and  other  juices,  it  passes  in  a  fluid  state  through  the  walls  of  the 
intestine,  where  it  becomes  part  of  the  blood.  As  blood  it  is  passed  on 
to  tissues,  such  as  muscle,  to  make  new  material  to  be  used  in  repairing 
that  which  is  used  up  during  the  flight  of  the  insect  or  to  be  oxidized  to 
release  energy  for  the  active  insect. 

Eyes.  —  A  considerable  part  of  the  surface  of  the  head  of  the  grass- 
hopper is  taken  up  by  the  compound  eyes.  Examination  with  a  lens 
shows  the  whole  surface  to  be  composed  of  tiny  hexagonal  spaces  called 
facets.  Each  facet  is  believed  to  be  a  single  eye,  with  perhaps  distinct 
vision  from  its  neighbor.  The  grasshopper  also  has  three  simple  eyes  on 
the  front  of  the  head.  The  simple  eyes  probably  are 
only  able  to  perceive  light  and  darkness.  The  sepa- 
rate units  of  the  compound  eye  probably  each  give  a 
separate  impression  of  light  and  color.  Thus  a  com- 
pound eye  is  most  favorable  for  perceiving  the  move- 
ment of  objects. 

Other  Sense  Organs.  —  The  segmented  feelers,  or 
antennce,  have  to  do  with  the  sense  of  touch  and  smell. 
The  eardrum,  or  tympanum,  of  the  grasshopper  is 
found  under  the  wing  on  the  first  segment  of  the  ab- 
domen. Covering  the  body  and  on  the  appendages, 
are  found  hairs  (sensory  hairs)  which  appear  to  make 
the  insect  sensitive  to  touch.  Thus  the  armor-covered 
animal  is  put  in  touch  with  its  surroundings. 

Nervous  System.  —  The  nerve  chain,  as  in  the  cray- 
fish, is  on  the  ventral  side  of  the  body.  As  in  the 
crayfish,  it  passes  around  the  gullet  near  the  head  to 
the  dorsal  side,  where  a  collection  of  ganglia  forms  the  brain.  Nerves 
leave  the  central  system  as  outgoing  fibers  which  bear  motor  impulses. 
Other  nerve  fibers  pass  inward,  and  produce  sensations.  These  are  called 
sensory  fibers. 


Longitudinal  section 
of  part  of  the  com- 
pound eye  of  an 
insect :  a,  facets ; 
c,  nerves. 


Life  History.  —  The  female  red-legged  locust  lays  its  eggs  by- 
digging  a  hole  in  the  ground  with  her  ovipositor,  or  egg-layer,  the 
modified  end  of  the  abdomen.  From  twenty  to  thirty  eggs  are 
laid  in  the  fall;  these  hatch  out  in  the  spring  as  tiny  wingless 
grasshoppers,  otherwise  like  the  adult.  As  in  the  crayfish,  the 
young  molt  in  order  to  grow  larger,  each  grasshopper  undergoing 
several  molts  before  reaching  the  adult  state.  No  great  change 
in  form  occurs,  the  metamorphosis  being  said  to  be  incomplete. 
In  the  fall  most  of  the  adults  die,  only  a  few  surviving  the  winter. 

Relatives  of  the  Locust.  —  Among  the  near  relatives  are  the 
brown  or  black  crickets,  cockroaches  and  "  waterbugs,"  the  katydid, 


THE  INSECTS 


237 


Part  of  the  ving  of  a  moth 
(aamia),  magnified  to  show 
the  arrangement  of  scales 
partly  nibbed  oflf. 


praying  mantis,  and  many  others.     All  of  the  above  insects  have 

the  hind  wings,  when  present,  folded  up  lengthwise  against  the  body 

when  at  rest,   mouth  parts  fitted   for 

biting,  and  an  incomplete  metamorpho- 
sis.   They  are  thus  placed  in  an  order 

called  Orthoptera  because  the  posterior 

wings   are   folded  straight  against  the 

body   when  at    rest    {orthos,   straight, 

pteron,  wing). 

The    Butterfly.  —  The    body  of    the 

butterfly,  as  that  of  the  grasshopper,  is 

composed  of  three  regions.     Compared 

with  the   grasshopper,  the  wings   and 

legs  show  the  greatest   differences   in 

structure.     The  legs  of  the  butterfly  are  relatively  smaller  and 

weaker  than  those  of 
the  grasshopper,  while 
the  wings  are  rela- 
tively larger  in  the 
first-named  insect. 
Evidently  the  butter- 
fly spends  much  of  its 
time  in  the  air. 

If  the  wing  is  rubbed 
with  the  finger,  dust 
comes  off  it,  leaving 
the  wing  transparent 
or  membrane-like. 
Under  the  microscope 
the  wing  is  seen  to  be 
covered  with  thou- 
sands of  little  colored 
scales,  each  of  which 
fits  into  a  socket  in 
the  wing.  These 
scales  cause  the  name 

Monarch  butterfly :  adults,  larva,  and  pupa  on  milk-       T         '^       f  (1        ' 

weed.     From  photograph  loaned  by  the  American      ^^P^^aoptera      {lepiS, 
Museum  of  Natural  History.  SCale,  pteron,  wing)   to 


238  THE  INSECTS 

be  given  to  this  order  of  insects.  The  long  proboscis,  a  sucking 
tube  through  which  the  insect  sucks  nectar  from  flowers,  is  an- 
other character  by  which  the  Lepidoptera  may  be  known. 

Life  History.  —  The  monarch  or  milkweed  butterfly  (Anosia 
plexippus)  is  one  of  our  commonest  insects.  Its  orange-brown, 
black-veined  wings  are  famihar  to  every  boy  or  girl  who  has  been 
outdoors  in  the  country  during  the  fall  months.  The  adult  female 
lays  her  eggs  in  the  late  spring  on  the  milkweed.  The  eggs,  tiny 
sugar-loaf-shaped  dots  a  twentieth  of  an  inch  in  length,  are  fas- 
tened singly  to  the  underside  of  milkweed  leaves.  Some  won- 
derful instinct  leads  the  animal  to  deposit  the  eggs  on  the  milkweed, 
for  the  young  feed  upon  no  other  plant.  Eggs  laid  in  May  hatch 
out  in  four  or  five  days  into  rapid-growing  caterpillars,  each  of 
which  will  molt  several  times  before  it  becomes  full  size.  These 
caterpillars  possess  in  addition  to  the  three  pairs  of  true  legs, 
additional  pairs  of  prolegs  or  caterpillar  legs.  The  animal  at  this 
stage  is  known  as  a  larva. 

Formation  of  Pupa.  —  After  a  life  of  a  few  weeks  a.t  most,  the 
caterpillar  stops  eating  and  begins  to  spin  a  tiny  mat  of  silk  upon 
a  leaf  or  stem.  It  attaches  itself  to  this  web  by  the  posterior  pair 
of  prolegs,  and  there  hangs  until  a  last  molt  (which  occurs  within 
twenty-four  hours  after  attachment)  gives  the  animal  the  form  it 
assumes  in  the  stage  known  as  the  chrysalis  or  pupa. 

The  Adult.  —  After  a  week  or  more  of  inactivity,  the  exoskeleton 
is  split  along  the  dorsal  side,  and  the  adult  butterfly  emerges.  At 
first  the  wings  are  soft  and  much  smaller  than  in  the  adult.  Within 
fifteen  minutes  to  half  an  hour  after  the  butterfly  emerges,  however, 
the  wings  are  full-sized,  having  been  pumped  full  of  blood. 

In  the  adult  form  the  animal  may  survive  the  winter.  The 
milkweed  butterfly  is  a  strong  flyer,  and  has  been  found  over  five 
hundred  miles  at  sea.  They  may  migrate  southward  upon  the 
approach  of  the  cold  weather.  Some  common  forms,  as  the 
mourning  cloak  (Vanessa  antiopa),  hibernate  in  the  North,  passing 
the  cold  weather  under  stones  or  overhanging  clods  of  earth. 

Comparison  between  a  Moth  and  a  Butterfly.  —  The  big  electric  light 
moth  cecropia  (Samia  cecropia)  is  an  insect  familiar  to  most  of  us.  In 
general  it  resembles  a  butterfly  in  structure.  Several  differences,  however, 
occur.     The  body  is  much  stouter  than  that  of  the  butterfly.     The  wings 


THE    INSECTS 


239 


and  body  appear  to  have  a  thicker  coating  of  hairs  and  scales,  and  the 
antennas  are  feathery.  The  position  of  the  wings  when  at  rest  forms 
another  easy  way  of  dis- 
tinguishing the  one  in- 
sect from  the  other. 
(See  Figures,  page  237.) 
Development.  The 
Egg.  —  The  eggs,  cream- 
colored  and  as  large  as  a 
pinhead,  are  deposited 
in  small  clusters  on  the 
underside  of  leaves  of 
the  food  plant.  The 
young  are  at  first  tiny 
black  caterpillars,  which 
later  change  color  to  a 
bluish  green,  with  projec- 
tions of  blue,  yellow,  and 
red  along  the  dorsal  side. 
The  Pupal  Stage.  — 
Unlike  the  butterfly,  the 
moth  passes  the  quies- 
cent stage  in  a  case  of 
silk  or  other  material 
called  a  cocoon.  The  co- 
coons of  cecropia  may 
be  found  in  the  fall  on 
willows  or  alders.  Such 
cocoons  found  in  mead- 
ows or  fields  are  usually 
larger  than  those  found  on  the  hillsides,  probably  because  of  a  difference 
in  the  food  supply  of  the  larva  which  spun  the  cocoon. 

If  the  cocoon  is  cut  open  lengthwise  (see  Figure),  the  dormant  insect  or 

chrysalis  will  be  found  to- 
gether with  the  cast-oflF  skin 
of  the  caterpillar  which  spun 
the  case. 

Silkworms.  —  The  Ameri- 
can silkworm  (Telea  polyphe- 
mus)  is  another  well-known 
mbth.  The  cocoons,  made 
in  part  out  of  the  leaves  of 
the  elm,  oak,  or  maple,  fall 
to  the  ground  when  the 
leaves  drop,  and   hence  are 


Life  history  of  the  cecropia  moth.  Above,  the  adult ; 
the  larva  (caterpillar)  in  center ;  the  pupal  case  to 
right,  below ;  the  same  cut  open  at  left,  below. 
From  photograph  loaned  by  the  American  Mu- 
seimi  of  Natural  History. 


Polyphemus,    one    half    natural    size, 
graphed  by  Davison. 


Photo- 


240  THE   INSECTS 

not  so  easily  found  as  those  of  the  cecropia.  This  moth  is  a  near  relative 
of  the  Chinese  silkworm,  and  its  silk  might  be  used  with  success  were  it 
not  for  the  high  rate  of  labor  in  this  country.  The  Chinese  silkworm  is 
now  raised  with  ease  in  southern  California.  China,  Japan,  Italy,  and 
France,  because  of  cheap  labor,  are  still  the  most  successful  silk-raising 
countries. 

Differences  Between  Moths  and  Butterflies 

Butterfly  Moth 

Antennae       threadlike,  usually         Antennae    feathery    or    threadlike, 

knobbed  at  tip.  never  knobbed. 

Fly  in  daytime.  Usually  fly  at  night. 

Wings    held    vertically  when    at         Wings  held  horizontally  or  folded 

rest.  over  the  body  when  at  rest. 

Pupa  naked.  Pupa  usually  covered  by  a  cocoon. 

Moths  and  butterflies  are  both  characterized  by  having  a  sucking 
proboscis,  membranous  wings  covered  with  scales,  and  both  undergo  a 
complicated  metamorphosis  or  change  of  form.  By  these  characters  we 
know  them  to  be  members  of  the  order  Lepidoptera. 

Diptera.  The  Typhoid  Fly.  —  This  name  has  been  recently  given 
to  the  common  house  fly  by  L.  O.  Howard,  the  Chief  of  the  Bu- 
reau of  Entomology,  United  States  Department  of  Agriculture. 


Life  history  of  house  flies,  showing  from  left  to  right  the  eggs,  larvaj,  pupae,  and 
adult  flies.     Photograph,  about  natural  size,  by  Overton. 

We  shall  later  see  with  what  reason  this  name  is  given.  The  body 
of  the  fly,  as  in  other  insects,  has  three  divisions.  The  membran- 
ous wings  appear  to  be  two  in  number,  a  second  pair  being  reduced 


THE    INSECTS 


241 


to  tiny  knobbed  hairs  called  balancers.    Their  function  is  seemingly 
that  of  equilibrium. 

The  head  is  freely  movable,  the  compound  eyes  being  extremely 
large.  Seemingly  the  fly  has  fairly  acute  vision.  Home  experi- 
ments can  be  easily  made  which  prove  its  keenness  of  scent  and 
caste.  It  is  well  equipped  to  care  for  itself  in  its  artificial  environ- 
ment in  the  house. 

The  mouth  parts  of  the  fly  are  prolonged  to  form  a  proboscis, 
which  is  tonguelike,  the  animal  obtaining  its  food  by  lapping  and 
sucking.  It  is  the  rubbing  of  this  file- 
like organ  over  the  surface  of  the  skin 
that  causes  the  painful  bite  of  the  horsefly. 

If  possible,  we  should  examine  the 
foot  of  a  fly  under  the  compound  mi- 
croscope. The  foot  shows  a  wonderful 
adaptation  for  clinging  to  smooth  sur- 
faces. Two  or  three  pads,  each  of  which 
bears  tubelike  hairs  that  secrete  a  sticky 
fluid,  are  found  on  its  under  surface.  It 
is  by  this  means  that  the  fly  is  able  to 
walk  upside  down.  Hooks  are  also  pres- 
ent which  doubtless  aid  in  locomotion 
in  this  position. 

Development.  —  The  development  of  the  typhoid  fly  is  extremely 
rapid.  A  female  may  lay  from  one  hundred  to  two  hundred  eggs. 
These  are  usually  deposited  in  filth  or  manure.  Dung  heaps 
about  stables,  ash  heaps,  garbage  cans,  and  fermenting  vegetable 
refuse  form  the  best  breeding  places  for  flies.  In  warm  weather, 
within  a  day  after  the  eggs  are  laid,  the  young  maggots,  as  the  larvae 
are  called,  hatch.  After  about  one  week  of  active  feeding,  these 
wormlike  maggots  become  quiet  and  go  into  the  pupal  stage, 
whence  under  favorable  conditions  they  emerge  within  less  than 
another  week  as  adult  flies.  The  adults  breed  at  once,  and  in  a 
short  summer  there  may  be  over  ten  generations  of  flies.  This 
accounts  for  the  great  number.  Fortunately  few  flies  survive  the 
winter. 

Other  Diptera.  —  Other  examples  of  this  group  are  the  mos- 
quitoes, of  which  more  will  be  said  hereafter;  the  Hessian  fly,  the 

HUNT.  ES.  BIO.  —  IG 


Foot  of    a  fly,  showing    the 
hooks,  hairs,  and  pads. 


242 


THE   INSECTS 


larvae  of  which  feeds  on  young  wheat;  the  botfly,  which  in  a 
larval  state  is  a  parasite  on  horses ;  the  dreaded  tsetse  fly  of  South 
Africa,  which  causes  disease  in  horses  and  cattle  by  means  of  the 
transference  of  a  parasitic  protozoan,  much  like  that  which  causes 
malaria  in  man ;  and  many  others. 

Among  the  few  flies  useful  to  man  may  be  mentioned  the  tachina 
flies,  the  larvae  of  which  feed  on  the  cutworm,  the  army  worm, 
and  various  other  kinds  of  injurious  caterpillars. 

Characters  of  the  Diptera.  —  Members  of  this  group  have  only 
one  pair  of  wings;  the  mouth  parts  are  fitted  for  sucking,  rasping, 
or  piercing,  and  they  pass  through  a  com- 
plete metamorphosis. 

Coleoptera.  Beetles.  —  Beetles  are  the  most 
widely  distributed  and  among  the  most  nu- 
merous of  all  insects.  There  are  over  one 
hundred  thousand  living  species. 

Any  beetle  will  show  the  following  charac- 
teristics: (1)  The  body  is  usually  heavy  and 
broad.  Its  exoskeleton  is  hard  and  tough,  the 
chitinous  body  covering  being  better  developed 
in  the  beetles  than  in  any  other  of  the  insects. 
(2)  The  three  pairs  of  legs  are  stout  and  rather 
short.  (3)  The  outer  wings  are  hard  and  fit 
over  the  under  wings  like  a  shield.  These 
sheathlike  wings  are  called  elytra.  (4)  The 
mouth  parts,  provided  with  an  upper  and  lower 
lip,  are  fitted  for  biting.  They  consist  of 
very  heavy  curved  pincher-shaped  mandibles,  which  are  provided  with 
palps. 

The  Life  History  of  a  Beetle.  —  The  June  beetle  (May  beetle)  and  potato 
beetle  are  excellent  examples.  May  beetles  lay  their  eggs  in  the  ground, 
where  they  hatch  into  cream-colored  grubs.  A  grub  differs  from  the  larva 
fly  or  maggot  in  possessing  three  pairs  of  legs.  These  grubs  Hve  in  bur- 
rows in  the  ground.  Here  they  feed  on  the  roots  of  grass  and  garden 
plants.  The  larval  form  remains  underground  for  from  two  to  three  years, 
the  latter  part  of  this  time  as  an  inactive  pupa.  During  the  latter  stage 
it  lies  dormant  in  an  ovoid  area  excavated  by  it.  Eventually  the  wings 
(which  are  budlike  in  the  pupa)  grow  larger,  and  the  adult  beetle  emerges 
fitted  for  its  life  in  the  open  air. 

Order  Hemiptera.  Bugs.  Characteristics.  —  The  cicada,  or,  as  it  is 
incorrectly  called,  the  locust,  is  a  familiar  insect  to  all.  Its  droning  song 
is  one  of  the  accompaniments  of  a  hot  day.     The  song  of  the  cicada  is 


Stag  beetle  :  a,  antenna;  e. 
eye ;  m,  mandible ;  p,  pal- 
pus. Photograph  one  half 
natural  size. 


THE    INSECTS 


243 


Cicada:  /,  adult  with  wings  spread,  showing  abdomen  (-46.),  head  (H.),  ihor&x 
iTh.) ;  2,  pupal  case,  showing  the  split  down  the  back ;  3,  ventral  view,  showing 
beak  (B.),  eye  (E.). 

produced  by  a  drumlike  organ  which  can  be  found  just  behind  the  last 
pair  of  legs.  The  sound  is  caused  by  a  rapid  vibration  of  the  tightly 
stretched  drumhead.  The  body  is  heavy  and  bulky.  The  wings,  four  in 
number,  are  relatively  small,  but  the  powerful  muscles  give  them  very 

rapid  movement.     The  anterior  wings  are  larger     

than  the  posterior.  The  legs  are  not  large  nor 
strong,  the  movement  when  crawling  being  slug- 
gish. One  of  the  characteristics  of  the  cicada, 
and  of  all  other  bugs,  is  that  the  mouth  parts  are 
prolonged  into  a  beak  with  which  the  animal  first 
makes  a  hole  and  then  sucks  up  the  juices  of  the 
plants  on  which  it  lives. 

Life  History.  —  The  seventeen-year  cicada 
lays  her  eggs  in  twigs  of  trees,  and  in  doing  this 
causes  the  death  of  the  twig.  The  young  leave 
the  tree  immediately  after  hatching,  burrow  under- 
ground, and  pass  from  thirteen  to  seventeen  years 
there,  depending  upon  the  species  of  cicada.  In 
the  South  this  period  is  shortened.  They  live  by 
sucking  the  juices  from  roots.  During  this  stage 
they  somewhat  resemble  the  grub  of  the  beetle 
(June  bug)  in  habits  and  appearance.  When 
they  are  about  to  molt  into  an  adult,  they  climb 
aboveground,  cling  to  the  bark  of  trees,  and  then 
crawl  out  of  the  skin  as  adults. 

Aphids.  —  The  aphids  are  among  the  most  in- 
teresting of  the  bugs.     They  are  familiar  to  all 


Maple  scale,  five  adults  and 
many  young.  From  pho- 
tograph, enlarged  twice, 
by  Davison. 


244 


THE  INSECTS 


as  the  tiny  green  lice  seen  swarming  on  the  stems  and  leaves  of  the  rose 
and  other  cultivated  plants.  They  suck  the  juices  from  stem  and  leaf. 
Plant  lice  have  a  remarkable  life  history.  Early  in  the  year  eggs  develop 
into  wingless  females,  which  produce  living  young,  all  females.  These  in 
turn  reproduce  in  a  similar  manner,  until  the  plant  on  which  they  live 
becomes  overcrowded  and  the  food  supply  runs  short.  Then  a  genera- 
tion of  winged  aphids  is  produced.  These  fly  away  to  other  plants,  and 
reproduction  goes  on  as  before  until  the  approach  of  cold  weather,  when 
males  and  females  appear.  Fertilized  eggs  are  then  produced  which  give 
rise  to  young  the  following  season. 

The  aphids  exude  from  the  surface  of  the  body  a  sweet  fluid  called 
honeydew.  This  is  given  off  in  such  abundance  that  it  is  estimated  if  an 
aphid  were  the  size  of  a  cow,  it  would  give  two  thousand  quarts  a  day. 
This  honeydew  is  greatly  esteemed  by  other  insects,  especially  the  ants. 
For  the  purpose  of  obtaining  it,  some  ants  care  for  the  aphids,  even  pro- 
viding food  and  shelter  for  them.  In  return  the  aphid,  stimulated  by  a 
stroking  movement  of  the  antenna  of  the  ant,  gives  up  the  honeydew  to 
its  protector. 

The  Order  Neuroptera 

The  Dragon  Fly.  —  The  dragon  fly  receives  its  name  because  it  preys 
on  insects.  It  eats,  when  an  adult,  mosquitoes  and  other  insects  which 
it  captures  while  on  the  wing.     Its  four  large  lacelike  wings  give  it  power 

of  very  rapid  flight,  while  its  long 
narrow  body  is  admirably  adapted 
for  the  same  purpose.  The  large 
compound  eyes  placed  at  the  sides 
of  the  head  give  keen  sight.  It 
possesses  powerful  jaws  (almost 
covered  by  the  upper  and  lower 
lips). 

The  long,  thin  abdomen  does 
not  contain  a  sting,  contrary  to 
the  belief  of  most  children. 
These  insects  deposit  their  eggs 
in  the  water,  and  the  fact  that 
they  may  be  often  seen  with  the 
end  of  the  abdomen  curved  down 
under  the  surface  of  the  water  in  the  act  of  depositing  the  eggs  has  given 
rise  to  the  belief  that  they  were  then  engaged  in  stinging  something.  The 
egg  hatches  into  a  form  of  larva  called  a  nymph,  which  in  the  dragon  fly 
is  characterized  by  a  greatly  developed  lower  lip.  When  the  animal  is  at 
rest,  the  lower  lip  covers  the  large  biting  jaws,  which  can  be  extended  so 
as  to  grasp  and  hold  its  prey.  The  nymphs  of  the  dragon  fly  take  oxygen 
out  of  the  water  by  means  of  gill-like  structures  placed  in  the  posterior 


Dragon  fly.     Notice  the  long  abdomen  and 
large  compound  eyes. 


THE  INSECTS 


245 


part  of  the  food  tube.  They  may  live  as  larvae  from  one  summer  to  as 
long  as  two  years  in  the  water.  They  then  crawl  out  on  a  stick,  molt  by 
sphtting  the  skin  down  the  back,  and  come  out  as  adults. 

A  nearly  related  form  is  the  damsel  fly.  This  may  be  distinguished 
from  the  dragon  fly  by  the  fact  that  when  at  rest  the  wings  are  carried 
close  to  the  abdomen,  while  in  the  dragon  fly  they  are  held  in  a  horizontal 
position. 

May  Flies.  —  Another  near  relative  of  the  dragon  fly  is  the  May  fly. 
These  insects  in  the  adult  stage  have  lost  the  power  to  take  food.  Most 
of  their  life  is  passed  in  the  larval  stage  in  the  water.  The  adults  some- 
times live  only  a  few  hours,  just  long  enough  to  mate  and  deposit  their 


The  Order  Hymenoptera 

We  have  already  learned  something  of  the  structure  of  the  bee,  an 
example  of  this  order.  Other  relatives  are  the  wasps,  ichneumons  (wasp- 
like insects  with  long  ovipositors),  and  the  ants.  The  structural  characters 
of  this  group  are  the  presence  of  two  pairs  of  membranous  wings,  the  mouth 
parte  being  fitted  for  biting  and  lapping.  All  undei^o  a  complete  meta- 
morphosis, the  young  being  helpless  wingless  creatures  somewhat  like  the 
maggots  of  the  fly.     Of  this  group  we  shall  learn  more  later. 

The  orders  of  insects  mentioned  above  are  only  some  examples  of  this 
very  large  group.  In  all  of  the  above  forms  we  have  seen  certain  like- 
nesses and  certain  differences  in  structure,  but  all  of  the  above  have  had 
three  body  divisions,  three  pairs  of  legs,  and  have  possessed  in  the  adult 
state  air  tubes  called  tracheae.  These  are  the  principal  characters  by 
which  we  may  identify  the  insects. 

Spiders  and  Myriapods.  —  Spiders  are  not  true  insects,  although  they 
are  nearly  allied  to  them. 
The  body  shows  the  same 
division  as  do  the  higher 
crustaceans,  cephalothorax 
and  abdomen  ;  four  pairs  of 
walking  legs  mark  another 
difference.  These  animals 
usually  have  four  pairs  of 
simple  eyes  and  breathe  by 
means  of  lunglike  sacs  in  the 
abdomen,  the  openings  of 
which  can  sometimes  be  seen 
just  behind  the  most  pos- 
terior pair  of  legs.  Another 
organ  possessed  by  the 
spider,  which  insects  do  not 
have    (except    in    a    larval 


Tarantula  on  its  back  :  p,  poison  fang ;  s,  spin- 
neret.    Reduced  from  photograph  by  Davi- 


246  THE  INSECTS 

form),  is  known  as  the  spinneret.  This  is  a  set  of  glands  which  secrete 
in  a  liquid  state  the  silk  which  the  spider  spins.  On  exposure  to  air, 
this  fluid  hardens  and  forms  a  very  tough  building  material  which  com- 
bines lightness  with  strength. 

Uses  and  Form  of  the  Web.  —  The  web-making  instinct  of  spiders 
forms  an  interesting  study.  Our  common  spiders  may  be  grouped  ac- 
cording to  the  kind  of  web  they  spin.  The  web  in  some  cases  is  used  as  a 
home  ;  in  others  it  forms  a  snare  or  trap.  In  some  cases  the  web  is  used 
for  ballooning,  spiders  having  been  noticed  clinging  to  their  webs  miles 
out  at  sea.  The  webs  seen  most  frequently  are  the  so-called  cobwebs. 
These  usually  serve  as  a  snare  rather  than  a  home,  some  species  remain- 
ing away  from  the  web.  Other  webs  are  funnel-shaped,  still  others  are  of 
geometrical  exactness,  while  one  form  of  spider  makes  its  home  under- 
ground, lines  the  hole  with  silk,  and  makes  a  trapdoor  which  can  be  closed 
after  the  spider  has  retreated  to  its  lair. 


A  poisonous  centipede  from  Texas.    Half  natural  size.     From  photograph  by  Davison. 

Myriapods.  —  We  are  all  familiar  with  the  harmless  and  common 
thousand  legs  found  under  stones  and  logs.  It  is  a  representative  of  the 
group  of  animals  known  as  the  millepedes.  These  animals  have  the  body 
divided  into  two  regions,  head  and  trunk,  and  have  two  pairs  of  legs  for 
each  body  segment.  The  centipedes,  on  the  other  hand,  have  only  one 
pair  of  legs  to  each  segment.  Both  are  representatives  of  the  class 
Myriapoda.  None  of  the  forms  in  the  eastern  part  of  the  United  States 
are  poisonous. 

Insects  and  Crustaceans  Compared.  —  Both  crustaceans  and 
insects  belong  to  a  great  group  of  animals  which  agree  in  that  they 
have  jointed  appendages  and  bodies,  and  that  they  possess  an 
exoskeleton.  This  group  or  phylum  is  known  as  the  Arthropoda. 
Spiders  and  myriapods  are  also  included  in  this  group. 

Insects  differ  structurally  from  crustaceans  in  having  three 
regions  in  the  body  instead  of  two.     The  number  of  legs  (three 


THE    INSECTS  247 

pairs)  is  definite  in  the  insects ;  in  the  crustaceans  the  number 
sometimes  varies  (as  in  the  Entomostraca),  but  is  always  more  than 
three  pairs.  The  exoskeleton,  composed  wholly  of  chitin  in  the 
insects,  is  usually  strengthened  with  lime  in  the  crustaceans. 
Both  groups  have  compound  eyes,  but  those  of  the  Crustacea  are 
staked  and  movable.  The  other  sense  organs  do  not  differ  greatly. 
The  most  marked  differences  are  physiological.  The  crustaceans 
take  in  oxygen  from  the  water  by  means  of  gills,  while  the  insects 
are  air  breathers,  using  for  this  purpose  air  tubes  called  trachece. 

The  young  of  both  insects  and  crustaceans  usually  undergo 
several  changes  in  form  before  the  adult  stage  is  reached.  They 
are  thus  said  to  pass  through  a  metamorphosis.  Both  insects  and 
crustaceans,  because  of  their  exoskeleton,  must  molt  in  order  to 
increase  in  bulk. 

Classification  of  Arthropoda 

Phylum  Arthropoda 

Class,  Crustacea.  Arthropods  with  limy  and  chitinous  exoskeleton,  rarely  more 
than  20  body  segments,  usually  breathing  by  gills,  and  having  two  pairs  of 
antennse. 

Subclass  I.  Entomostraca.,  Crustacea  with  a  variable  number  of  segments, 
chiefly  small  forms  with  simple  appendages.  Some  degenerate  or  parasitic. 
Examples:    barnacles,  water  flea  (Daphnia),  and  copepod  (Cyclops). 

Subclass  II.     Malacostraca.     Usually  large    Crustacea    having    nineteen    pairs 
of  appendages.     Examples:    American   lobster   (Homarus  Americanns),  crab 
(Cancer),  and  shrimp  (Paloemonetes) . 
Class,  Hexapoda  (insects).     Arthropoda  having  chitinous  exoskeleton,  breathing 
by  air  tubes  (trachea),  and  having  three  distinct  body  regions. 

Order,  ^p<era  (without  wings).     Several  wingless  forms.     Examples:   springtails. 

Order,  Orthoptera  (straight  wings).     Example:   Rocky  Mountain  locust. 

Order,  Lepidoptera  (scale  wings).    Examples :  cabbage  butterfly,  cecropia  moth. 

Order,  Diptera  (two  wings).     Examples:    fly,  mosquito. 

Order,  Hemiptera  (half  wing) .     Examples :    all  true  bugs,  plant  lice,  and  cicada. 

Order,  Neuroptera  (nerve  wings).     Examples:    May  fly,  dragon  fly. 

Order,  Coleoptera  (shield  wings).     Examples:    beetles. 

Order,  Hymenoptera  (membrane  wings).  Examples:  bees,  wasps,  ants. 
Class,  Arachnida.  Arthropoda  with  head  and  thorax  fused.  Six  pairs  of  appen- 
dages. No  antennae.  Breathing  by  both  lung  sacs  (spiders)  or  trachese.  Ex- 
amples :  spiders  and  scorpions. 
Class,  Myriapoda.  Arthropoda,  having  long  bodies  with  many  segments;  one 
or  two  pairs  of  appendages  to  each  segment.  Breathing  by  means  of  tracheae. 
Example :   centipede. 

An  exercise  for  field  work  with  a  simple  key  for  identification  of  orders  will  b^ 
found  in  the  Labratory  Manual,  Prob.  XXX. 


248  THE  INSECTS 


Reference  Books 
elementaby 

Sharpe,  A  Laboratory  Maniud  for  the  Solution  of  Problems  in  Biology.    American 

Book  Company. 
Comstock,  J.  H.,  Insect  Life.     D.  Appleton  and  Company. 
Davison,  Practical  Zoology.     American  Book  Company. 
Howard,  L.  O.,  The  Insect  Book.     Doubleday,  Page,  and  Company. 
Hunter,  S.  J.,  Elementary  Stvdies  in  Insect  Life.     Crane  and  Company. 
Needham,  Outdoor  Studies.     American  Book  Company. 

ADVANCED 

Comstock,  J.  H.,  An  Introduction  to  Entomology.     Comstock  Publishing  Company. 
Emerton,  The  Structure  and  Habits  of  Spiders.     Knight  and  Millett. 
Kellogg,  V.  L.,  American  Insects.     Henry  Holt  and  Company. 


XX.    GENERAL    CONSIDERATIONS   FROM    THE    STUDY    OF 

INSECTS 

Problem  XXXI,    How  insects  hecame  winners  in  life's  race. 
{Laboratory  Manual,  Prob.  XXXI.) 

(a)  Protective  resemblance. 

(b)  Aggressive  resemblance. 

(c)  Mimicry. 

id)  Communal  life. 
ie)   Symbiosis. 
(/)  Parasitism. 

Insects  are  by  far  the  most  numerous  of  all  animals.  It  is  esti- 
mated that  there  are  more  species  of  insects  than  of  all  other 
species  of  animals  upon  the  globe.  Why  should  insects  come 
to  have  existed  in  so  mu3h  greater  numbers  than  other  animals? 
We  cannot  explain  this,  but  some  light  is  thrown  on  the  problem 
when  we  consider 
some  of  the  ways 
in  which  insects 
have  become 
winners  in  life's 
race. 

Protective  Re- 
semblance.  — 
When  we  re- 
member that  the 
chief  enemies  of 
insects  are  birds 
and  other  ani- 
mals which  use 
them  as  food,  we 
can  see  that  the 

insect's  power  of  rapid   flight  must   have  been  of  considerable 
importance  in  escaping  from  enemies.     But  other  means  of  pro- 

249 


The    walking    stick    on    a    twig,    showing    protective    re- 
semblance. 


250    CONSIDERATIONS  FROM  STUDY   OF  INSECTS 


tection  are  seen  when  we  examine  insects  in  their  native  haunts. 
We  have  noted  that  various  animals,  such  as  the  earthworm 
and  crayfish,  escape  observation  because  they  have  the  color 
of  their  surroundings.  Insects  give  many  interesting  examples 
of  protective  coloration  or  protective  resemblance.  The  grass- 
hopper   is    colored    hke    the    grass    on    which    it    Hves.     The 

katydid,    with    its    green    body    and 

^^^       wings,  can  scarcely  be  distinguished 

^^HB       from  the   leaves  on  which   it   rests. 

^t^^^^^J^^^^^f       The  walking  stick,  which  resembles 

m^^^^Kt^^^^^^'      ^^^  twigs  on  which  it  is  found,  and 

^^^H^H^PH^fP        the  walking-leaf  insect  of  the  tropics, 

^!^^W^|\^^^^  are  other  examples. 

One  example  frequently  quoted  is 
the  dead-leaf  butterfly  of  India. 
This  insect  at  rest  resembles  a  dead 
leaf  attached  to  a  limb ;  in  flight,  be- 
cause of  its  vivid  colors,  it  is  con- 
spicuous. The  underwing  moth  is 
another  example  of  a  wonderful  sim- 
ulation of  the  background  of  bark  on 
which  the  animal  rests  in  the  daytime. 
At  night  the  brightly  colored  under- 
wings  probably  give  a  signal  to  others 
of  the  same  species.  The  beautiful 
luna  moth,  in  color  a  delicate  green, 
rests  by  day  among  the  leaves  of  the 
hickory.  The  small  measuring  worms 
stand  out  stiff  upon  the  branches  on 
which  they  crawl,  thus  simulating  lateral  twigs.  Hundreds  of 
other  examples  might  be  given. 

This  likeness  of  an  animal  to  its  immediate  surroundings  has 
already  been  noted  as  protective  resemblance. 

Aggressive  Resemblance.  —  Sometimes  animals  which  resemble 
their  surroundings  are  thus  better  able  to  catch  their  prey.  The 
polar  bear  is  a  notable  example.  Some  insects  are  thus  colored. 
The  mantis,  shown  in  the  figure,  has  strongly  built  forelegs,  with 
which  it  seizes  and  holds  insects  on  which  it  preys.     The  mantis 


The    underwing    moth ;    above, 
flying ;  below,  at  rest  on  bark. 


CONSIDERATIONS   FROM   STUDY   OF   INSECTS    251 


has  the  color  of  its  immediate  sur- 
roundings, and  is  thus  enabled  to 
seize  its  prey  before  the  latter  is 
aware  of  its  presence.  Many  other 
examples  could  be  given. 

Warning  Coloration  and  Protective 
Mimicry.  —  Some  insects  are  ex- 
tremely unpleasant,  both  to  smell  or 
to  taste,  while  others  are  provided 
with  means  of  defense  such  as  poison 
hairs  or  stings.  Such  animals  are 
almost  always  brightly  colored  or 
marked  as  if  to  warn  animals  to  keep 
off  or  take  the  consequences.  Ex- 
amples of  insects  which  show  warn- 
ing by  color  may  be  seen  in  many 
examples  of  beetles,  especially  the 
spotted  ladybirds,  potato  beetles,  and 
the  like.  Wasps  show  yellow  bands, 
while  many  forms  of  caterpillars  are  conspicuously  marked  or  colored. 

Some  insects,  especially  caterpillars,  are  brightly  colored  and 
protrude  horns,  or  pretend  to  sting  when  threatened  with  attack. 
These  animals  evidently  mimic  animals  which  really  are  protected 

by  a  sting  or  by  poison, 


Mantis,  showing  aggressive  re- 
semblance. 


WW 


although  this  mimicry 
is  not  voluntary  on 
the  part  of  the  insect. 
One  of  the  best-known 
cases  of  insect  mim- 
icry is  seen  in  the  case 
of  the  imitation  of  the 

Monarch  and  \'iceroy  butterflies  :    the  latter  (at  the      monarch     butterfly    by 
right)  is  a  mimic.  the  viceroy. 

The  monarch  but- 
terfly {Anosia  plexippus)  is  an  example  of  a  race  which  has 
received  protection  from  enemies  in  the  struggle  for  life,  because 
of  its  nauseous  taste  and,  perhaps,  because  its  caterpillar  feeds 
on  plants  of  no  commercial  value. 


252    CONSIDERATIONS   FROM  STUDY  OF  INSECTS 


Another  butterfly,  less  favored  by  nature,  resembles  the  monarch 
in  outward  appearance.  This  is  the  viceroy  (Basilarchia  archippus) . 
It  seems  probable  that  in  the  early  history  of  the  species  called 
viceroy  some  of  this  edible  form  escaped  from  the  birds  because 
they  resembled  in  color  and  form  the  species  of  inedible  monarchs. 
These  favored  individuals  produced  new  butterflies  which  re- 
sembled the  monarch  more  closely.  So  for  generation  after  genera- 
tion the  ones  which  were  most  like  the  inedible  species  were  left, 
the  others  becoming  the  food  of  birds.  Ultimately  a  species  of 
butterflies  was  formed  that  owed  its  existence  to  the  fact  that  it 
resembled  another  more  favored  species.  In  this  way  nature  selects 
the  animals  which  can  exist  upon  the  earth.     Many  other  examples 

of  mimicry  may  be  found 
among  insects;  one  of  the 
easiest  to  find  is  the  locust 
borer,  shown  in  the  Figure. 
Some  flies  imitate  bees,  and 
thus  escape  capture. 

The  chief  insect  enemies 
are  the  birds,  and  from  these 
the  most  effective  protection 
seems  to  be  hairs  on  the 
body.  Few  birds  eat  hairy 
caterpillars  of  any  species;  fortunately,  however,  the  hairy 
larvse  of  the  gypsy  moth,  a  serious  pest,  are  eaten  by  no  less  than 
thirty-one  species  of  birds.  The  odors  or  ill  flavors  of  insects  seem 
to  be  generally  protective,  but  stinging  insects  do  not  appear  to  be 
protected  from  all  birds,  flycatchers  and  swallows  habitually  feeding 
on  the  bees  and  wasps. ^ 

Communal  Life  among  Insects.  —  Insects  are  of  especial  in- 
terest to  man  because  among  certain  species  a  system  of  social 
life  has  arisen  comparable  to  that  which  exists  among  men.  In 
connection  with  this  communal  life,  nature  has  worked  out  a 
division  of  labor  which  is  very  remarkable.  This  can  be  seen  in 
tracing  out  the  lives  of  several  of  the  insects  which  live  in  com- 
munities. 


Hornet  mimicked  by  locust  borer,  a  beetle. 


1  See  Judd,  J.  S.,  "The  Efficiency  of  Some  Protective  Adaptations  in  securing 
Insects  from  Birds,"  American  Naturalist,  Vol.  33,  pages  461-484. 


CONSIDERATIONS  FROM  STUDY   OF  INSECTS    253 

Solitary  Wasps.  —  Some  bees  and  wasps  lead  a  solitary  existence. 
The  solitary  and  digger  wasps  do  not  live  in  communities.  Each  female 
constructs  a  burrow  in  which  she  lays  eggs  and  rears  her  young.  The 
young  are  fed  upon  spiders  and  insects  previously  caught  and  then  stung 
into  insensibility.  The  nest  is  closed  up  after  food  is  supplied,  and  the 
young  later  gnaw  their  way  out.  In  the  life  history  of  such  an  insect  there 
is  no  communal  life. 

Bumblebee.  —  In  the  life  history  of  the  big  bumblebee  we  see  the 
beginning  of  the  community  instinct.  Some  of  the  female  bees  (known 
as  queens)  survive  the  winter  and  lay  their  eggs  the  following  spring  in  a 
mass  of  pollen,  which  has  been  previously  gathered  and  placed  in  a  hole 
in  the  ground.  The  young  hatch  as  larvae,  then  pupate,  and  finally  be- 
come workers,  or  females.  In  the  working  bee  the  egg-laying  apparatus, 
or  ovipositor,  is  modified  to  be  used  as  a  sting.  The  workers  bring  in 
pollen  to  the  queen,  in  which  she  lays  more  eggs.  Several  broods  of 
workers  are  thus  hatched  during  a  summer.  In  the  early  fall  a  brood  of 
males  or  drones,  and  egg-laying  females  or  queens,  are  produced  instead 
of  workers.  By  means  of  these  egg-producing  females  the  brood  is 
started  the  foUowing  year. 

The  Honeybee.  —  The  most  wonderful  communal  life  is  seen 
among  the  honeybees.^ 

The  honeybee  in  a  wild  state  makes  its  home  in  a  hollow  tree ; 
hence  the  term  "  bee  tree."  In  the  hive  the  colony  usually  consists 
of  a  queen,  or  egg-laying  female,  a  few  hundred  drones,  or  males, 
and  several  thousand  working  females,  or  workers.  The  colonies 
vary  greatly  in  numbers,  in  a  wild  state  there  being  fewer  in 
the  colony.  The  division  of  labor  is  well  seen  in  a  hive  in  which 
the  bees  have  been  living  for  some  weeks.  The  queen  does  noth- 
ing except  lay  eggs,  sometimes  laying  three  thousand  eggs  a  day 
and  keeping  this  up,  during  the  warm  weather,  for  several  years. 
She  may  lay  one  million  eggs  during  her  hfe.  She  does  not,  as  is 
popularly  believed,  rule  the  hive,  but  is  on  the  contrary  a  captive 
most  of  her  life.  Most  of  the  eggs  are  fertilized  by  the  sperm  cells 
of  the  males;   the  unfertilized  eggs  develop  into  males  or  drones. 

^  Their  daily  life  may  be  easily  watched  in  the  schoolroom,  by  means  of  one  of 
the  many  good  and  cheap  observation  hives  now  made  to  be  placed  in  a  window 
frame.  Directions  for  making  a  small  observation  hive  for  school  work  can  be  found 
in  Hodge,  Nature  Study  and  Life,  Chap.  XIV.  Bulletin  No.  1,  U.S.  Department 
of  Agriculture,  entitled  The  Honey  Bee,  by  Frank  Benton,  is  valuable  for  the  ama- 
teur beekeeper.  It  may  be  obtained  for  twenty-five  cents  from  the  Superintendent 
of  Documents,  Union  Building,  Washington,  D.C. 


254    CONSIDERATIONS   FROM   STUDY   OF  INSECTS 


After  a  sjiort  existence  in  the  hive  the  drones  are  usually  driven  out 
by  the  T\^rkers.     The  fertiUzed  eggs  may  develop  into  workers,  but 

if  the  young  larva  is  fed  with 

a  certain  kind  of  food,  it  will 
develop  into  a  young  queen. 

The  cells  of  the  comb  are 
built  by  the  workers  out  of 
wax  secreted  from  the  under 
surface  of  the  bodies.  The 
wax  is  cut  off  in  thin  plates 
by  means  of  the  wax  shears 
between  the  two  last  joints 
of  the  hind  legs.  These  cells 
are  used  by  the  queen  to 
place  her  eggs  in,  one  to 
each  cell,  and  the  young  are 
hatched  after  three  days,  to 
begin  life  as  footless  white 
grubs. 

For  a  few  days  they  are 

fed  on  partly  digested  food 

called  bee  jelly,  regurgitated 

the  workers.     Later   they  receive   pollen 

little   of    this   mixture,    known    as    bee 


Hornets'  nest,  open  to  show  the  cells  of  the 
comb.    Photograph  by  Overton. 


from  the  stomach  of 
and    honey   to  eat.     A 


Honeybees  :    a,  drone ;    b,  worker ;    c,  queen.     Photograph  by  Davison. 


bread,  is  then  put  into  the  cell,  the  lid  covered  with  wax  by 
the  working  bees,  and  the  young  larvae  allowed  to  pupate.     After 


CONSIDERATIONS   FROM  STUDY   OF  INSECTS     255 

about  two  weeks  of  quiescence  in  the  pupal  state,  the  adult  worker 
breaks  out  of  the  cell  and  takes  her  place  in  the  hive,  first  caring  for 
the  young  as  a  nurse,  later  making  excursions  to  the  open  air  after 
food  as  an  adult  worker. 

If  new  queens  are  to  be  produced,  several  of  the  cell  walls  are 
broken  down  by  the  workers,  making  a  large  ovoid  cell  in  which 
one  egg  develops.  The  young  bee  in  this  cell  is  fed  during  its  whole 
larval  life  upon  bee  jelly,  and  grows  to  a  much  larger  size  than  an 
ordinary  worker.  When  a  young  queen  appears,  great  excitement 
pervades  the  community ;  the  bees  appear  to  take  sides ;  some  re- 
main with  the  young  queen  in  the  hive,  while  others  follow  the  old 
queen  out  into  the  world.  Here  they  usually  settle  around  the 
queen,  often  hanging  to  the  Hmb  of  a  tree.  This  is  called  swarming. 
This  instinct  is  of  vital  importance  to  the  bees,  as  it  provides  them 
with  a  means  of  forming  a  new  colony.  For  while  the  bees  are 
swarming,  certain  of  the  workers,  acting  as  scouts,  determine  on  a 
site  for  their  new  home ;  and,  if  undisturbed,  the  bees  soon  go  there 
and  construct  their  new  hive.  A  swarm  of  domesticated  bees, 
however,  may  be  quickly  hived  in  new  quarters. 

We  have  already  seen  (pages  42  and  43)  that  the  honeybee 
gathers  nectar,  which  she  swallows,  keeping  the  fluid  in  her  crop 
until  her  return  to  the  hive.  Here  it  is  regurgitated  into  cells  of 
the  comb.  It  is  now  thinner  than  what  we  call  honey.  To  thicken 
it,  the  bees  swarm  over  the  open  cells,  moving  their  wings  very 
rapidly,  thus  evaporating  some  of  the  water  in  the  honey.  A  hive 
of  bees  have  been  known  to  make  over  thirty-one  pounds  of  honey 
in  a  single  day,  although  the  average  record  is  very  much  less  than 
this. 

Ants.  —  Ants  are  the  most  truly  communal  of  all  the  insects.  Their  life 
history  and  habits  are  not  so  well  known  as  those  of  the  bee,  but  what  is 
known  shows  even  more  wonderful  specialization.  The  inhabitants  of  a 
nest  may  consist  of  wingless  workers,  which  in  some  cases  may  be  of  two 
kinds,  and  winged  males  and  females. 

Ant  larvae  are  called  grubs.  They  are  absolutely  helpless  and  are 
taken  care  of  by  nurses.  The  pupae  may  often  be  seen  taken  out  in  the 
mouths  of  the  nurse  ants  for  sun  and  air.  They  are  mistakenly  called 
ants'  eggs  in  this  stage. 

The  colonies  consist  of  underground  galleries  with  enlarged  store- 
rooms, nurseries,  etc.     The  ants  are  especially  fond  of  honeydew  secreted 


256    CONSIDERATIONS   FROM   STUDY   OF  INSECTS 


by   the  aphids,   or  plant  lice.     Some  species  of  ants  provide  elaborp.te 
stables  for  the  aphids,  commonly  called  ants'  cows,  supplying  with  food 

and  shelter  and  taking  the  honeydew 
as  their  reward.  This  they  obtain  by 
licking  it  from  the  body  of  the  aphids. 
A  Western  form  of  ant,  found  in  New 
Mexico  and  Arizona,  rears  a  scale  in- 
sect on  the  roots  of  the  cactus  for  this 
same  purpose. 

It  is  probable  that  some  species 
of  ants  are 
among  the 
most  warlike 
of  any  in- 
robber  ants,  which 


i 


\  "^*^^=   YA  Food. 
\  i 


Diagram  of  an  artificial  ants'  nest : 
8,  moistened  sponge.  (After  Miss 
Fielde.)! 


sects.  In  the  case  of  the 
live  entirely  by  war  and  pillage,  the  workers 
have  become  modified  in  structure,  and  can  no 
longer  work,  but  only  fight.  Some  species  go 
further  and  make  slaves  of  the  ants  preyed 
upon.  These  slaves  do  all  the  work  for  their 
captors,  even  to  making  additions  to  their  nest 
and  acting  as  nurses  to  their  young. 

The  entire  communal  life  of  the  ants  seems 
to  be  based  upon  the  perception  of  odor.  If 
an  ant  of  the  same  species  but  from  a  different 


Ants  and  their  "cows,' 
aphids. 


1  A  successful  nest  for  the  schoolroom  is  made  and  describad  by  Miss  Adele  M. 
Fielde.     See  the  Biological  Bulletin,  Vol.  VII,  No.  4,  September,  1904. 

The  floor  of  the  nest  is  a  pane  of  window  glass  six  by  ten  inches.  Build  a  wall 
by  cementing  with  crockery  cement  four  half-inch  strips  of  thicker  glass,  and  upon 
these  cement  four  more  strips,  making  the  wall  at  least  one  quarter  of  an  inch  high. 
The  space  inside  is  divided  by  one  or  two  partitions  built  the  same  as  the  outer  wall. 
Spaces  should  be  allowed  for  communication  between  chambors.  The  whole  outer 
surface  of  the  nest  thus  made  may  be  covered  with  black  paper  to  make  it  opaque. 
A  lining  of  Turkish  toweUng  is  glued  to  the  top  of  the  wall.  The  cover,  which  rests 
on  the  toweling,  should  be  either  of  glass  made  opaque,  or  better,  of  glass  (such 
as  ruby  glass  of  dark  rooms)  that  will  exclude  most  of  the  ultra-violet  light  rays. 
It  is  best  to  provide  a  separate  roof  for  each  chamber.  Ants  need  moisture,  so  that 
a  small  bit  of  moist  sponge  should  be  kept  in  the  room  where  the  ants  live.  The 
food  chamber,  where  bits  of  cake,  banana,  apple,  or  other  food  mixed  with  honey 
or  molasses,  are  placed,  should  also  be  kept  moist. 

To  stock  such  a  nest,  dig  up  a  small  colony  and  transfer  them,  along  with  some 
earth,  to  the  schoolroom.  To  separate  the  ants  from  the  earth,  place  them  with  the 
earth  on  a  little  island  of  wood  in  a  basin  of  water.  On  one  side  of  the  island  place 
a  glass  plate,  and  shade  this  plate  by  a  piece  of  opaque  paper  raised  slightly  above 
the  glass.  The  ants  soon  remove  themselves  and  their  young  to  the  dark  area, 
and  may  then  be  transferred  to  the  nest.  Ant  colonies  have  been  kept  for  three 
or  four  years  in  such  a  nest. 


CONSIDERATIONS   FROM   STUDY  OF   INSECTS    257 

nest  be  put  into  another  colony,  it  will  be  set  upon  and  either  driven  out 
or  killed.  Ants  never  really  lose  their  community  odor ;  those  absent  for 
a  long  time,  on  returning,  will  be  easily  distinguished  by  their  odor,  and 
eagerly  welcomed  by  the  members  of  the  nest.  The  talking  of  ants  (when 
they  stop  each  other,  when  away  from  the  nest,  to  communicate)  is  evi- 
dently a  process  of  smelling,  for  they  caress  each  other  with  the  antennsB, 
the  organs  with  which  odors  are  perceived. 


Symbiosis.  —  We  have  already  seen  that  plants  and  animals 
frequently  live  in  a  state  of  partnership  or  relation  of  mutual  help. 
Such  a  state  is  known  as  a  symbiotic  relation.  The  keeping  of 
the  aphids  by  the  ants  which  use  them  as  " cows"  is  an  example  of 
this  relation  among  two  species  of  insects.  The  ants  provide  pro- 
tection and  sometimes  food;  the  aphids  give  up  the  honey  dew  of 
which  the  ants  are  so  fond. 

But  a  wider  symbiotic  relation  exists  directly  between  the  flower- 
ing plants  and  the  insects.  We  all  know  the  very  great  service 
done  the  plants  by  the  pollination  of  the  flower  by  the  insects,  and 
we  know  that  the  return  is  the  supply  of  pollen  and  nectar  as  food 
for  the  insects.  If  it  were  not  for 
the  bees,  wasps,  and  butterflies, 
it  is  safe  to  predict  that  many 
of  our  fruit  crops  would  bo 
almost  entire  failures.  Do  you 
know  why  ? 

Parasitism.  —  One  of  the  near 
relatives  of  the  bee  called  the 
ichneumon  fly  does  man  indi- 
rectly considerable  good  because 
of  its  habit  of  laying  its  eggs 
and  rearing  the  young  in  the 
bodies  of  caterpillars  which  are 
harmful  to  vegetation.  Some 
of  the  ichneumons  even  bore 
into  trees  in  order  to  deposit 
their  eggs  in  the  larvae  of  wood- 
boring  insects.  It  is  safe  to  say 
that  by  the  above  means  the  ichneumons  save  millions  of  dollars 
yearly  to  this  country. 

HUNT.  ES.  BIO. 17 


Thalcssa  lx)ring  in  an  a.sh  tnc  t(;  deposit 
its  eggs  in  the  burrow  of  a  horntail 
larva,  a  wood  borer.  From  photo- 
graph, natural  size,  by  Davison. 


258    CONSIDERATIONS  FROM  STUDY  OF  INSECTS 

Unfortunately,  not  all  insect  parasites  do  good.  Animals  of  all 
kinds,  but  especially  birds,  are  infested  with  lice  and  fleas.  The 
ticks  are  well  known  for  the  harm  they  do,  while  the  larvae  of  the 
botflies  which  live  in  the  bodies  of  various  mammals,  as  the  horse 
and  sheep  and  cattle,  are  insect  parasites  which  do  much  harm. 

Problem  XXXII.  Some  relations  of  insects  toman.    iLahoro/- 
tory  Manual,  Proh.  XXXII.) 
{d)  With  reference  to  disease. 

(b)  With  reference  to  destruction  of  property. 

(c)  With  reference  to  benefit  to  man. 

The  Relation  of  Insects  to  Mankind.  —  We  already  have  seen 
this  relation  is  twofold,  harmful  or  beneficial.  The  harmful  relation 
may  affect  man  directly,  as  when  human  disease  is  carried  by 
insects,  or  it  may  be  indirect,  as  in  the  case  of  damage  to  crops, 
trees,  stored  food,  or  clothing.  The  first  relations,  naturally  of 
more  importance,  as  malaria  and  typhoid  fever,  two  extremely 
prevalent  diseases,  may  be  largely  due  to  insects.  There  are 
probably  one  million  cases  of  ''  chills  and  fever  "  in  the  Southern 
states  alone  every  year.  Malaria  and  typhoid  could  be  largely 
eradicated  if  there  were  no  mosquitoes  or  flies.  It  is  therefore 
evident  that  a  careful  study  of  the  habits  of  these  insects  is  worth 
our  while. 

The  Malarial  Mosquito.  —  Fortunately  for  mankind,  not  all 
mosquitoes  harbor  the  small  one-celled  parasite  (a  protozoan) 
which  causes  malaria.  The  harmless  mosquito  (culex)  may  be 
usually  distinguished  from  the  mosquito  which  carries  malaria 
{anopheles)  by  the  position  taken  when  at  rest.  (See  page  197.) 
Culex  lays  eggs  in  tiny  rafts  of  one  hundred  or  more  eggs  in  any 
standing  water;  thus  the  eggs  are  distinguished  from  the  eggs  of 
anopheles,  which  are  not  in  rafts.  Rain  barrels,  gutters,  or  old 
cans  may  breed  in  a  short  time  enough  mosquitoes  to  stock  a 
neighborhood.  The  larvae  are  known  as  wigglers.  They  breathe 
through  a  tube  in  the  posterior  end  of  the  body,  and  may  be 
recognized  by  their  peculiar  movement  when  on  their  way  to  the 
surface  to  breathe.  The  fact  that  both  larvse  and  pupae  take  air 
from  the  surface  of  the  water  makes  it  possible  to  kill  the  mosquito 


CONSIDERATIONS   FROM   STUDY  OF   INSECTS    259 

during  these  stages  by  pouring  oil  on  the  surface  of  the  water  where 
they  breed.  The  introduction  of  minnows,  gold  fish,  or  other 
small  fish  which  feed  upon  the  larvae  in  the  water  where  the 
mosquitoes  breed  will  do  much  in  freeing  a  neighborhood  from 
this  pest.  Draining  swamps  or  low  land  which  holds  water  after 
a  rain  is  another  method  of  extermination. 

Since  the  beginning  of  historical  times,  malaria  has  been  preva- 
lent in  regions  infested  by  mosquitoes.  The  ancient  city  of  Rome 
was  so  greatly  troubled  by  periodic  outbreaks  of  malarial  fever 
that  a  goddess  of  fever  came  to  be  worshiped  in  order  to  lessen 
the   severity  of  what   the  inhabitants   believed  to  be  a  divine 


Three  pupse  and  two  larvae  of  mosquitoes  at  the  surface  of  the  water,  l)reathing. 
The  black  line  is  the  water  surface.  Photograph  from  life,  twice  natural  size, 
by  Davison. 


visitation.  At  the  present  time  the  malaria  of  Italy  is  being  suc- 
cessfully fought  and  conquered  by  the  draining  of  the  mosquito- 
breeding  marshes.  By  a  little  carefully  directed  oiling  of  water 
a  few  boys  may  make  an  almost  uninhabitable  region  absolutely 
safe  to  live  in.  Why  not  try  it  if  there  are  mosquitoes  in  your 
neighborhood  ? 

Yellow  Fever  and  Mosquitoes.  —  Another  disease  which  has 
been  proved  to  be  carried  by  mosquitoes  is  yellow  fever.  In  the 
year  1878  there  were  125,000  cases  and  12,000  deaths  in  the  city 
of  Memphis,  Tenn.,  alone,  with  thousands  of  deaths  in  other 
Southern  cities.  During  the  French  occupation  of  the  Panama 
Canal  zone  the  work  was  at  a  standstill  part  of  the  time  because 
of  the  ravages  of  yellow  fever. 


260    CONSIDERATIONS  FROM  STUDY  OF  INSECTS 


But  to-day  this  is  changed,  and  yellow  fever  is  under  almost 
complete  control,  both  here  and  wherever  the  mosquito  {stegomyia) 
which  carries  yellow  fever  exists.  The  mosquitoes  are  prevented 
from  biting  persons  having  yellow  fever ;  for  in  this  way  only  can 
the  disease  be  spread.  Drainage  and  oiling  of  breeding  places, 
and  screening  of  all  windows,  are  helping  to  build  the  Panama 
Canal. 

The  Typhoid  Fly  a  Pest.  —  The  common  fly  is  recognized  as  a 
pest  the  world  over.     Fhes  have  long  been  known  to  spoil  food 

through  their  filthy  habits,  but 
it  is  more  recently  that  the 
very  serious  charge  of  spread 
of  diseases,  caused  by  bacteria, 
has  been  laid  at  their  door. 
In  a  recent  experiment  two 
young  men  from  the  Connecti- 
cut Agricultural  Station  found 
that  a  single  fly  might  carry 
anywhere  from  500  to  6,600,000 
bacteria,  the  average  number 
being  over  1,200,000.  Not  all 
of  these  germs  are  harmful, 
but  they  might  easily  include 
those  of  typhoid  fever,  tuber- 
culosis, summer  complaint,  and 
possibly  other  diseases.  A  recent  pamphlet  published  by  the 
Merchants'  Association  in  New  York  city  shows  that  the  rapid 
increase  of  flies  during  the  summer  months  has  a  definite 
correlation  with  the  increase  in  the  number  of  cases  of  summer 
complaint.  Observations  in  other  cities  seem  to  show  the 
increase  in  number  of  typhoid  cases  in  the  early  fall  is  due,  in 
part  at  least,  to  the  same  cause.  It  has  been  estimated  that  the 
loss  caused  from  this  disease  is  in  a  single  year  $350,000,000  in 
the  United  States  alone.  A  large  part  of  this  loss  is  indirectly  due 
to  the  typhoid  fly. 

Other  Diseases  due  to  Insects.  —  The  bubonic  plague,  the 
dreaded  scourge  of  the  East,  is  probably  carried  to  man  by  fleas. 
The  sleeping  sickness  of  Africa  has  already  been  mentioned  (page  197) 


■iii'.iiiiiiimiiiiiiiiiiiiMiiii'/itiiiiiiJi,'inii)iiii'7nr 
Showing  how  flies  may  spread  disease  by 
means  of  contaminating  food. 


CONSIDERATIONS  FROM  STUDY   OF   INSECTS    261 

as  carried  by  the  tsetse  fly.  Several  other  diseases  of  man  and 
many  other  animals,  especially  cattle,  are  carried  by  flies.  The 
Texas  fever  of  cattle  is  carried  by  a  cattle  tick,  an  animal  closely 
allied  to  the  insects. 


^ 

^  ^ 

^ 

When  flies  are  plentiful,  there  is  a  considerable  increase  in  the  numl>or  of  cases 
of  illness  among  babies. 

Economic  Loss  from  Insects.  —  The  money  value  of  crops, 
forest  trees,  stored  foods,  and  other  material  destroyed  annually 
by  insects  is  beyond  belief.  It  is  estimated  that  they  get  one  tenth 
of  the  country's  crops,  at  the  lowest  estimate  a  matter  of  some 
$300,000,000  yearly. 

'*  A  recent  estimate  by  experts  put  the  yearly  loss  from  forest  insect 
depredations  at  not  less  than  $100,000,000.  The  common  schools  of 
the  country  cost  in  1902  the  sum  of  $235,000,000,  and  all  higher  institu- 
tions of  learning  cost  less  than  $o0,000,000,  making  the  total  cost  of  edu- 
cation in  the  United  States  considerably  less  than  the  farmers  lost  from 
insect  ravages. 

"  Furthermore,  the  yearly  losses  from  insect  ravages  ag^egate  nearly 
twice  as  much  as  it  costs  to  maintain  our  army  and  navy;  more  than 
twice  the  loss  by  fire ;  twice  the  capital  invested  in  manufacturing  agri- 
cultural implements;  and  nearly  three  times  the  estimated  value  of  the 
products  of  all  the  fruit  orchards,  vineyards,  and  small  fruit  farms  in  the 
country."  —  Slingerland. 

In  1874-1876  the  damage  to  crops  by  the  Rocky  Mountain 
locust  has  been  estimated  at  $200,000,000.  At  certain  times,  these 
locusts  migrate  from  Colorado,  Wyoming,  and  Dakota,  where  they 
seem  always  to  be  found,  and  descend  in  countless  millions  upon  the 
grain  fields  to  the  eastward.  Fortunately,  these  invasions  have 
been  rare  in  recent  years.    The  total  value  of  all  farm  and  forest 


262    CONSIDERATIONS  FROM  STUDY  OF   INSECTS 


crops,  excluding  animal  products,  in  New  York,  is  perhaps 
$150,000,000,  and  the  one  tenth  that  the  insects  get  is  worth 
$15,000,000.  It  may  seem  incredible  that  it  costs  such  a  sum  to 
feed  New  York's  injurious  insects  every  year,  but  it  is  an  average 
of  $66  for  each  of  the  227,000  farms  in  the  state ;  and  there  are 
few  farms  where  the  crops  are  not  lessened  more  than  this  amount 
by  insects. 

Insects  which  damage  Garden  and  other  Crops.  —  The  grass- 
hoppers have  been  mentioned  as  among  the  most  destructive  of 
these.  The  larvae  of  various  moths  do  considerable  harm  here, 
especially  the  "  cabbage  worm,"  the  various  caterpillars  of  the 
hawk  moths  which  feed  on  grape  and  tomato  vines,  the  cutworm, 
a  feeder  on  all  kinds  of  garden  truck,  the  corn  worm,  a  pest  on  corn, 
cotton,  tomatoes,  peas,  and  beans.  The  last  annually  damages 
the  cotton  crop  to  the  amount  of  several  millions  of  dollars. 

Among  the  beetles  which  are  found  in  gardens  is  the  potato  beetle, 
which  destroys  the  potato  plant.     This  beetle  formerly  lived  in 
Colorado  upon  a  wild  plant  of  the  same  family  as  the  potato,  and 
came  east  upon  the  introduction  of  the  potato  into  Colorado,  evi- 
dently   preferring     culti- 
vated forms  to  wild  forms 
of      this      family.       The 
asparagus    and   cucumber 
beetles   are   also  often  in 
evidence. 

The  one  beetle  doing 
by  far  the  greatest  harm 
in  this  country  is  the 
cotton-boll  weevil.  Im- 
ported from  Mexico,  since 
1892  it  has  spread  over 
eastern  Texas  and  into 
Louisiana.  The  beetle 
lays  its  eggs  in  the  young 
cotton  fruit  or  boll,  the 
larvai  feeding  upon  the 
substance  within  the  boll.  It  is  estimated  that  if  unchecked  this 
j^est  would  destroy  yearly  one  half  of  the  cotton  crop,  a  matter 


Cotton-boll  weevil :   a,  larva  ;   b,  pupa ;  c,  adult. 
Photograph,  enlarged  four  times,  by  Davison. 


CONSIDERATIONS   FROM   STUDY   OF   INSECTS    263 


of  $250,000,000.  Fortunately,  the  United  States  Department  of 
Agriculture  are  at  work  on  the  problem,  and,  while  they  have  not 
found  any  way  of  exterminating  the  beetle  as  yet,  it  has  been 
found  that,  by  planting  more  hardy  varieties  of  cotton,  the  crop 
matures  earlier  and  ripens  before  the  weevils  have  increased  in 
sufficient  numbers  to  destroy  the  crop  (see  page  62). 

The  bugs  are  among  our  most  destructive  insects.  The  most 
familiar  examples  of  our  garden  pests  are  the  squash  bug ;  the 
chinch  bug,  which  yearly  does  damage  estimated  at  $20,000,000,  by 
sucking  the  juice  from  the  leaves  of  grain;  and  the  plant  lice,  or 
aphids. 

Some  aphids  are  extremely  destructive  to  vegetation.  One,  the 
grape  Phylloxera,  yearly  destroys  immense  numbers  of  vines  in 
the  vineyards  of  France,  Germany,  and  California. 

The  Hessian  fly,  the  larvae  of  which  live  on  the  wheat  plant,  was 
introduced  accidentally  by  the  Hessians  in  their  straw  bedding 
during  the  Revolution,  and  has  become  one  of  our  most  serious  insect 
pests. 

Insects  which  harm  Fruit  and  Forest  Trees.  —  Great  damage  is 
done  annually  by  the  larvie  of  moths.  Massachusetts  has  already 
spent  over  $3,000,000  in  trying  to  ex- 
terminate the  imported  gypsy  moth. 
The  codling  moth,  which  bores  into 
apples  and  pears,  is  estimated  to  ruin 
yearly  $3,000,000  worth  of  fruit  in 
New  York  alone,  which  is  by  no  means 
the  most  important  apple  region  of  the 
United  States.  Among  these  pests, 
the  most  important  to  the  dweller  in 
a  large  city  is  the  tussock  moth,  which 
destroys  our  shade  trees.  The  cater- 
pillar may  easily  be  recognized  by  its 
hairy,  tufted  red  head.  The  eggs  are 
laid  on  the  bark  of  shade  trees  in  what 
look  like  masses  of  foam.  (See  Figure.) 
By  collecting  and  burning  the  egg  masses  in  the  fall,  we  may 
save  many  shade  trees  the  following  year. 

Other  enemies  of  the  shade  trees  are  the  fall  webworm,  the  forest 


Female  tussock  moth  which  has 
just  emerged  from  the  cocoon 
at  the  left,  upon  which  it  has 
deposited  over  two  hundred 
eggs.  Photograph,  slightly- 
enlarged,  by  Davison. 


264    CONSIDERATIONS   FROM   STUDY   OF   INSECTS 


caterpillar,  and  the  tent  caterpillar;   the  last  spins  a  tent  which 

serves  as  a  "shelter  in  wet  weather. 

The  larvae  of  some  moths  damage  the  trees  by  boring  into  the 

wood  of  the  tree  on  which  they  live.     Such  are  the  peach,  apple, 

and  other  fruit-tree  borers  com- 
mon in  our  orchards.  Some 
species  of  beetles  produce  bor- 
ing larvse  which  eat  their  way 
into  trees  and  then  feed  upon 
the  sap  of  the  tree.  Many 
trees  in  our  Adirondack  Forest 
Reserve  annually  succumb  to 
these  pests.  Many  trees  are 
killed  because  the  beetle  girdles 
the  tree,  cutting  through  the 
tubes  in  the  cambium  region. 
Most  fallen  logs  will  repay 
bore    between    the    bark    and 


Larva    of    tussock    moth.      Photograph, 
natural  size,  by  Davison. 


a    search    for    the    larvse    which 
wood. 

i  Among  the  bugs  most  destructive  to  trees  are  the  scale  insect 
and  the  plant  lice,  or  aphids.  The  San  Jos6  scale,  a  native  of  China, 
was  introduced  into  the  fruit  groves  of  California  about  1870  and 
has  spread  all  over  the  country.  It  lives  upon  numerous  plants, 
and  is  one  of  the  worst  pests  this  country  has  seen.  It  is  interest- 
ing to  know  that  a  ladybird  beetle,  which  has  also  been  imported, 
is  the  most  effective  agent  in  keeping  this  pest  in  check. 

Insects  of  the  House  or  Storehouse.  —  The  weevils  are  the 
greatest  pests,  frequently  ruining  tons  of  stored  corn,  wheat,  and 
other  cereals.  Roaches  feed  on  almost  any  kind  of  breadstuffs 
as  well  as  on  clothing.  The  carpet  beetle  is  a  recognized  foe  of  the 
housekeeper,  the  larvse  feeding  upon  all  sorts  of  woolen  material. 
The  larvse  of  the  clothes  moth  do  an  immense  amount  of  damage 
to  stored  clothing  especially.  Fleas,  lice,  and  especially  bedbugs 
are  among  man's  personal  foes.^ 

Beneficial  Insects.  —  Fortunately  for  mankind,  many  insects 
are  found  which  are  of  use  because  they  either  prey  upon  injurious 

1  Directions  for  the  treatment  of  these'  pests  may  be  found  in  pamphlets  issued 
by  the  U.S.  Department  of  Agriculture. 


CONSIDERATIONS  FROM  STUDY   OF   INSECTS    265 

insects  or  become  parasites  upon  them,  eventually  destroying 
them.  The  ichneumon  flies  are  examples  already  mentioned. 
They  undoubtedly  do  much  in  keeping  down  the  nimiber  of  de- 
structive caterpillars. 

Several  beetles  are  of  value  to  man.  Most  important  of  these  is 
the  natural  enemy  of  the  orange-tree  scale,  the  lady  bug,  or  lady- 
bird beetle.  In  New  York  state  it  may  often  be  found  feeding 
upon  the  plant  hce,  or  aphids,  which  hve  on  rosebushes.  The 
carrion  beetles  and  many  water  beetles  act  as  scavengers.  The 
sexton  beetles  bury  dead  carcasses  of  animals.  Ants  in  tropical 
countries  are  particularly  useful  as  scavengers. 

Insects,  besides  pollinating  flowers,  often  do  a  service  by  eating 
harmful  weeds.  Thus  many  harmful  plants  are  kept  in  check. 
We  have  noted  that  they  spin  silk,  thus  forming  clothing,  that 
in  some  cases  they  are  preyed  upon,  and  support  an  enormous 
multitude  of  birds,  fishes,  and  other  animals  with  food.  Make 
a  balance  sheet  showing  the  benefits  and  harm  done  man  by 
insects. 

How  the  Damage  done  by  Insects  is  Controlled.  —  The  com- 
bating of  insects  by  the  farmer  is  controlled  and  directed  by  two 
bodies  of  men,  both  of  which  have  the  same  end  in  view.  These 
are  the  Bureau  of  Entomology  of  the  United  States  Department 
of  Agriculture  and  the  various  state  experiment  stations. 

The  Bureau  of  Entomology  works  in  harmony  with  the  other 
divisions  of  the  Department  of  Agriculture,  giving  the  time  of  its 
experts  to  the  problems  of  controlling  insects  which,  for  good  or 
ill,  influence  man's  welfare  in  this  country.  Such  problems  as  the 
destruction  of  the  malarial  mosquito  and  control  of  the  typhoid 
fly ;  the  destruction  of  harmful  insects  by  the  introduction  of  their 
natural  enemies,  plant  or  animal ;  the  perfecting  of  the  honeybee 
(see  Hodge,  Nature  Study  and  Life,  page  240),  and  the  introduction 
of  new  species  of  insects  to  pollinate  flowers  not  native  to  this  coun- 
try (see  Blastophaga,  page  45),  are  some  to  which  these  men  are 
now  devoting  their  time. 

All  the  states  and  territories  (except  Indian  Territory)  have, 
since  1888,  established  state  experiment  stations,  which  work  in 
cooperation  with  the  government  in  the  war  upon  injurious  insects. 
These  stations  are  often  connected  with  colleges,  so  that  young 


266    CONSIDERATIONS   FROM  STUDY   OF   INSECTS 

men  who  are  interested  in  this  kind  of  natural  science  may  have 
opportunity  to  learn  and  to  help. 

The  good  done  by  these  means  directly  and  indirectly  is  very 
great.  Bulletins  are  published  by  the  various  state  stations 
and  by  the  Department  of  Agriculture,  most  of  which  may  be 
obtained  free.  The  most  interesting  of  these  from  the  high 
school  standpoint  are  the  Farmers'  Bulletins,  issued  by  the  De- 
partment of  Agriculture,  and  the  Nature  Study  pamphlets  issued  by 
the  Cornell  University  in  New  York  state. 

Reference  Books 
elementary 

Sharpe,  A  Laboratory  Manual  for  the  Solution  of  Problems  in  Biology.  American 
Book  Company. 

Craigin,  Our  Insect  Friends  and  Foes.    G.  P.  Putnam's  Sons. 

C^a^3^  Insects  and  their  Near  Relatives  and  Birds.  J.  Blakiston's  Son  and  Com- 
pany. 

Dahlgren,  The  Malarial  Mosquito.  Guide  Leaflet  27,  American  Museum  of  Natural 
History. 

Davison,  Practical  Zoology.     American  Book  Company. 

Dickinson,  Moths  and  Butterflies.     Henry  Holt  and  Company. 

Doane,  Insects  and  Disease.     Henry  Holt  and  Company. 

Farmers'  Bulletins,  45,  59,  70,  78,  99,  155. 

Howard,  L.  O.,  Insects  as  Carriers  of  Disease.  Year  Book,  U.S.  Department  of 
Agriculture,    1902. 

Howard,  L.  O.,  Mosquitoes.    McClure,  Phillips,  and  Company. 

Lubbock,  Bees,  Ants,  and  Wasps.     D.  Appleton  and  Company. 

ADVANCED 

Bulletins  of  Division  of  Entomology,  1,  4,  5,  12,  16,  19,  23,  33,  34,  35,  36,  47,  48,  51. 
Folsom,  Entomology  with  Reference  to  its  Biological  and  Economic  Aspects.      P.  Blaki- 
ston's Son  and  Company. 
Sanderson,  E.  D.,  Insects  injurious  to  Staple  Crops.     John  Wiley  and  Sons. 
Wheeler,  Ants.     The  MacmUlan  Company. 


XXI.  THE  MOLLUSKS 


rroblem  XXXIII  {OptlotMil) .  A  study  ofmollushs  and  their 
eneinies  tcith  reference  to  tJielr  economic  importance.  {.LaJboro/- 
tory  Manual,  Prdb.  XXXIII.) 

To  the  average  high  school  pupil  a  clam  or  oyster  on  the  **  half  shell " 
is  a  familiar  object.  The  soft  "  body  "  of  the  animal  lying  between  the 
two  protecting"  valves  "  of  the  shell  gives  the  name  to  this  group  (Latin  mol- 
lis—  soft).  Mostmollusks  have  a  limy  shell,  either  bivalve  (two-valved),  as 
the  oyster,  clam,  mussel,  and  scallop,  or  univalve,  as  in  the  snail.  Usually 
the  univalve  shell  is  spiral  in  form,  some  of  nature's  most  beautiful  objects 
being  the  spiral  shells  of  some  marine  forms.  Still  other  moUusks,  for 
example,  the  garden  slug,  have  no  external  shell  whatever. 

This  limy  shell  envelope  when  present,  is  formed  from  the  outer  edge  and 
surface  of  a  deUcate  body  covering  called  the  mantle.  The  mantle  may  be 
found  in  the  opened  oyster  or  clam 
sticking  close  to  the  inside  of  the 
valve  of  the  shell  in  which  the  body 
rests.  Between  the  mantle  and  the 
body  of  the  clam  or  oyster  is  a  space, 
the  mantle  cavity.  In  the  space  hang 
the  gills,  plateUke  striated  structures. 
By  means  of  cilia  on  the  inner  surface^ 
of  the  mantle  and  on  the  gills  a  con- 
stant cmrent  of  water  is  maintained 
through  the  mantle  cavity  bearing 
oxygen  to  the  gills  and  carbon  dioxide 
away.  This  current  of  water  passes, 
in  most  mollusks,  into  and  out  from 

the  mantle  cavity  through  the  siphons,  the  muscular  tubes  forming  the 
*'  neck "  of  the  **  soft  clam  "  being  an  example  of  such  an  organ. 

The  food  of  clams  or  oysters  consists  of  tiny  organisms,  plant  and 
animal,  which  are  carried  in  the  current  of  water  to  the  mouth  of  the 
animal,  this  water  current  being  maintained  in  part  by  the  action  of  ciha 
on  the  palps  or  Uplike  flaps  (p.  269)  surrounding  the  mouth.  A  single 
muscular  foot  aids  in  locomotion  when  the  animal  moves  about.  Many 
mollusks,  as  the  oyster,  are  fixed  when  adult. 

The  shallow  water  of  bays  and  other  quiet  bodies  of  salt  water  where 
clams  and  oysters  live,  Uterally  swarm  with  tiny  plants.  The  conditions 
for  the  growth  of  such  plants  is  ideal.  Water  from  the  rivers  contain- 
ing organic  waste  and  depositing  daily  its  load  of  mud  on  the  bottom 

267 


Fulgar,  a  univalve  mollusk  common  in 
Long  Island  Sound,  which  does  much 
harm  by  boring  into  the  shells  of 
edible  mollusks. 


268 


THE  MOLLUSKS 


gives  one  basis  for  the  support  of  these  plants.  The  carbon  dioxide  from 
the  thousands  of  species  of  fish,  mollusks,  crustaceans,  worms,  and  other 
forms  of  animal  life  gives  another  source  of  raw  food  material  for  the 
plant.  The  sunlight  penetrating  through  the  shallow  waters  supplies  the 
energy  for  making  the  food.  Thus  conditions  are  ideal  for  rapid  multi- 
plication ;  hence  the  water  becomes  alive  with  all  kinds  of  plant  life, 
especially  the  lower  forms.  Among  these  plants  are  always  found  bac- 
teria, both  harmless  and  harmful.  Mollusks  feed  upon  these  plants,  in- 
cluding the  bacteria  ;  man  feeds  on  the  mollusks,  and,  if  he  eats  them  raw, 
may  eat  living  bacteria  as  well.  Thus  disease  might  result,  and,  as  a  mat- 
ter of  fact,  epidemics  of  typhoid  fever  have  been  traced  to  such  a  source. 
Some  Common  Mollusks.  —  The  fresh-water  clam,  a  common  resi- 
dent in  shallow  water  in  inland  ponds  and  rivers,  although  not  useful 

for  food  to  man,  has  become 
the  source  of  a  very  impor- 
tant industry.  The  making 
of  pearl  buttons  has  so  de- 
pleted the  number  of  adult 
clams  in  our  Middle  West 
that  the  state  and  United 
States  governments  have  un- 
dertaken the  study  of  the 
life  habits  of  these  animals 
with  a  view  to  restocking  the 
rivers.  The  development  of 
the  fresh-water  clam  or 
mussel  is  complicated.  The  egg  develops  into  a  free-swimming  larval 
form  which  fastens  to  the  gills  of  a  fish  and  there  lives  as  a  parasite  until 
almost  mature.  Then  it  drops  off  and  begins  life  in  the  sand  of  the  river 
or  lake  where  it  lives. 

The  Oyster.  —  The  chief  difference  between  the  oyster  and  the  clam 
lies  in  the  fact  that  the  oyster  is  fastened  by  one  valve  to  some  solid  ob- 
ject, while  the  clam  or  fresh-water  mussel 
moves  about.  This  results  in  an  asymmetry 
in  the  shell  of  the  oyster. 

Oysters  are  never  found  in  muddy 
localities,  for  in  such  places  they  would  be 
quickly  smothered  by  the  sediment  in  the 
water.  They  are  found  in  nature  cUnging 
to  stones  or  on  shells  or  other  objects  which 
project  a  little  above  the  bottom.  Here 
food  is  abundant  and  oxygen  is  obtained  from  the  water  surrounding 
them.  Hence  oyster  raisers  throw  oyster  shells  into  the  water  and  the 
young  oysters  attach  themselves. 

In  some  parts  of  Europe  and  this  country  where  oysters  are  raised  ar- 


Shell  of  fresh-water  clam,  the  left  half  polished  to 
show  the  prismatic  layer  from  which  buttons 
are  made. 


Shell  of  oyster,   showing  asym- 
metry. 


THE  MOLLUSKS 


269 


tificially,  stakes  or  brush  are  sunk  in  shallow  water  so  that  the  young 
oyster,  which  is  at  first  free-swimming,  may  escape  the  danger  of  smoth- 
ering on  the  bottom.  After  the  oysters  are  a  year  or  two  old,  they  are 
taken  up  and  put  down  in  deeper  water  as  seed  oysters.  At  the  age  of 
three  and  four  years  they  are  ready  for  the  market. 

The  oyster  industry  is  one  of  the  most  profitable  of  our  fisheries. 
Nearly  $65,000,000  a  year  has  been  derived  during  the  last  decade  from 
such  sources.  Hundreds  of  boats  and  thousands  of  men  are  engaged  in 
dredging  for  oysters.  Three  of  the  most  important  of  our  oyster  grounds 
are  Long  Island  Sound,  Narragansett  Bay,  and  Chesapeake  Bay. 

Sometimes  oysters  are  artificially  "  fattened  "  by  placing  them  on  beds 
near  the  mouths  of  fresh-water  streams.  Too  often  these  streams  are  the 
bearers  of  much  sewage,  and  the  oyster,  which  lives  on  microscopic  organ- 
isms, takes  in  a  number  of  bacteria  with  other  food.  Thus  a  person  might 
become  infected  with  the  typhoid  bacillus  by  eating  raw  oysters.  It  is 
evident  that  state  and  city  supervision  ought  to  be  exercised  with  refer- 
ence not  only  to  the  sale  of  shellfish  which  comes  from  contaminated 
localities,  but  also  to  prevent  the  growth  of  oysters  or  other  mollusks  in 
the  neighborhood  of  the  openings  of  sewers  or  sewage-bearing  rivers. 

Clams.  —  Other  bi- 
valve mollusks  used  for 
food  are  clams  and  scal- 
lops. Two  species  of 
the  former  are  known  to 
New  Yorkers,  one  as 
the  "round,"  another  as 
the  "long"  or  "soft- 
shelled  "  clams.  The 
former  ( Venus  merce- 
neria)  was  called  by  the 
Indians  "  quahog,"  and 
is  still  so  called  in  th(^ 
Eastern  states.  The 
blue  area  of  its  shell 
was  used  by  the  Indians 
as  wampum,  or  money. 
The  quahog  is  now  ex- 
tensively used  as  food. 
The  "long"  clam  {Mya 
arenaria)  is  considered 
better  eating  by  the 
inhabitants  of  Massa- 
chusetts and  Rhode 
Island.  This  clam  was  highly  prized  as  food  by  the  Indians.  The  clam 
industries  of  the  eastern  coast  aggregate  nearly  SI, 000,000  a  year. 


Round  clam  {Venus  merceneria)  :  A  AM,  anterior  ad- 
ductor muscle ;  ARM,  anterior  retractor  muscle ; 
PAM,  posterior  adductor  muscle;  PRM,  posterior 
retractor  muscle;  F,  foot;  C,  cloacal  chamber; 
IS,  incurrent  siphon;  FS.,  excurrent  siphon; 
EO,  heart;  G,  gills;  M,  mantle;  DGL,  digestive 
glands ;  *S,  stomach ;  /,  intestine ;  P,  palp ;  R,  pos- 
terior end  of  digestive  tract. 


270 


THE   MOLLUSKS 


Scallop.  —  The  scallop,  another  moUuscan  delicacy,  forms  an  impor- 
tant fishery.  Only  the  single  adductor  muscle  is  eaten,  whereas  in  the 
clam  the  soft  parts  of  the  body  are  used  as  food. 

Pearls  and  Pearl  Formation.  —  Pearls  are  prized  the  world  over.  It 
is  a  well-known  fact  that  even  in  this  country  pearls  of  some  value  are 
sometimes  found  within  the  shells  of  such  common  bivalves  as  the  fresh- 
water mussel  and  the  oyster.  Most  of  the  finest,  however,  come  from 
the  waters  around  Ceylon.  If  a  pearl  is  cut  open  and  examined  carefully, 
it  is  found  to  be  a  deposit  of  the  mother-of-pearl  layer  of  the  shell  around 
some  central  structure.  It  has  been  believed  that  any  foreign  substance, 
as  a  grain  of  sand,  might  irritate  the  mantle  at  a  given  point,  thus  stimu- 
lating it  to  secrete  around  the  substance.  It  now  seems  likely  that  most 
perfect  pearls  are  due  to  the  growth  within  the  mantle  of  the  clam  or 
oyster  of  certain  parasites,  stages  in  the  development  of  a  flukeworm.  The 
irritation  thus  set  up  in  the  tissue  causes  mother-of-pearl  to  be  deposited 
around  the  source  of  irritation,  with  the  subsequent  formation  of  a  pearl. 

I  Gastropods.  —  Snails,  whelks,  slugs,  and  the 

^^^  ^  like   are    called    gastropods,    because    the    foot 

^■Hfcjjk^^^  occupies  so  much  space  that  most  of  the  organs 

^^^^^^Bt"^^  of  the  body,  including  the 

^^^Bjjjj^^^  stomach,   are   covered  by 

^^^Hf  it.     Such  animals  are  par- 

■j^P  tially  covered  by  a  more 

or    less    spirally    formed 


Forest  snail,  showing  the  two 
tentacles  with  an  eye  on 
the  end  of  each.  From 
photograph  by  Davison. 


shell  which  has  but  one 
valve.  In  most  gastro- 
pods the  body  is  spirally 
twisted  in  the  shell.  In 
the  garden  slug,  the  man- 
tle does  not  secrete  an  external  shell,  and  the  naked 

body  is  symmetrical. 

Gastropods  of    various    species    do    considerable 

damage,  some  in  the  garden,  where  they  feed  upon 

young  plants,  others  in  the  sea,  where  they  bore  into 

the  shells  of  other  living  moUusks  in  order  to  get 

out  the  soft  part  of  the  body  which  they  use  as  food. 
Cephalopods.  —  Another    class    of    mollusks   are 

those   known    as    cephalopods.       The   name    "ceph- 

alopod"  means  head-footed.     As  the  Figure  shows, 

the  mouth  is  surrounded  with  a  circle  of  tentacles. 

The  shell  is  internal  or  lacking,  the  so-called  pen  of 

the  cuttlefish  being  all  that  remains  of  the  shell  in 

that  form.     A  cuttlefish  is  strangely  modified  for  the 

life  it  leads.     It  moves  rapidly  through  the  water  by  squirting  water  from 

the  siphon.      It  can  seize  its  prey  with  the  suckers  on  the  long  tentacles 


The  squid.    One  fourth 
natural  size. 


THE  MOLLUSKS 


271 


and  tear  it  in  pieces  by  means  of  its  homy,  parrotlike  beak.  It  is  pro- 
tected from  its  enemies  and  is  enabled  to  catch  its  prey  because  of  its 
ability  to  change  color  quickly.  In  this  way  the  animal  simulates  its 
surroundings.  The  cuttlefish  has  an  ink  bag  near  the  siphon  which 
contains  the  black  sepia.  A  few  drops  of  this  ink  squirted  into  the  water 
may  efifectually  hide  the  animal  from  its  enemy. 

To  this  group  of  animals  belongs  also  the  octopus,  or  devilfish,  a  ceph- 
alopod  known  to  have  tentacles  over  thirty  feet  in  length,  the  paper 
nautilus  and  the  pearly  nautilus,  the  latter  made  famous  by  our  poet 
Holmes. 

Habitat  of  the  Mollusks.  —  Mollusks  are  found  in  almost  all  parts  of 
the  earth  and  sea.  They  are  more  abundant  in  temperate  localities  than 
elsewhere,  but  are  found  in  tropical  and  arctic  countries.  They  are  found 
in  all  depths  of  water,  but  by  far  the  greatest  number  of  species  live  in 
shallow  water  near  the  shore.  The  cephalopods  live  near  the  surface  of 
the  ocean,  where  they  prey  upon  small  fish.  The  food  supply  evidently 
determines  to  a  large  extent  where  the  animal  shall  live.  Some  mollusks 
are  scavengers ;  others  feed  on  living  plants. 

We  have  found  in  the  forms  of  mollusks  studied  that  almost  all  mol- 
lusks live  in  the  water.  There  is  one  great  group  which  forms  a  general 
exception  to  this,  certain  of  the  snails  and  plugs  called  pulmonates.  But 
even  these  animals  are  found  in  damp  locahties,  and  at  the  approach  of 
drought  they  become  inactive,  remaining  within  the  shell.  The  Euro- 
pean snail  ( Helix  -pomatia)  imported  to  this  country  as  a  table  delicacy 
exists  for  months  by  plugging  up  the  aperture  to  the  shell  with  a  mass  of 
slimy  material  which  later  hardens,  thus  protecting  the  soft  body  within. 

Economic  Importance.  —  In  general  the  mollusks  are  of  much  economic 
importance.  The  bivalves  especially  form  an  important  source  of  our  food 
supply.  Many  of  the 
mollusks  also  make  up 
an  important  part  of  the 
food  supplj^  of  bottom- 
feeding  fishes.  On  the 
other  hand,  some  mol- 
lusks, as  natica,  bore  into 
other  moUusk  shells  and 
eat  the  animal  thus  at- 
tached. Some  boring 
mollusks,  for  example 
the  shipworm  ( Teredo 
navalis),  do  much  dam- 
age, especially  to 
wharves,  as  they  make 
their  home  in  piles.     Still  others  bore  holes  in  soft  rock  and  live  there. 

The  shells  of  mollusks  are  used  to  a  large  extent  in  manufactures  and 


Piece  of  timber,  showing  holes  bored  by  the  shipworm. 


272 


THE  MOLLUSKS 


in  the  arts,  while  they  form  a  money  basis  still  in  parts  of  the  world. 
Sepia  comes  from  the  cuttlefish. 

The  Starfish.  —  By  all  means  the  most  important  enemy  of  the  oyster 
and  other  salt-water  mollusks  is  the  starfish.  The  common  starfish,  as  the 
name  indicates,  is  shaped  like  a  five-pointed  star.  A  limy  skeleton  which  is 
made  up  of  thousands  of  tiny  plates  gives  shape  to  the  body  and  arms. 

Slow  movement  is  effected 
by  means  of  tiny  suckers, 
called  tube  feet.  Breathing 
takes  place  through  the  skin. 
The  mouth  is  on  the  under 
surface  of  the  animal,  and, 
when  feeding,  the  stomach  is 
protruded  and  wrapped  around 
its  prey.  The  body  of  the 
starfish,  as  well  as  that  of  the 
sea  urchin  and  others  of  this 
group,  is  spiny;  hence  the 
name  Echinoderm  (spiny- 
skinned)  is  given  to  the 
group. 

Food  of  the  Starfish.— 
Starfish  are  enormously  de- 
structive of  young  clams  and 
oysters,  as  the  following  evi- 
dence, collected  by  Professor 
A.  D.  Mead  of  Brown  Uni- 
versity, shows.  A  single  star- 
fish was  confined  in  an  aqua- 
rium with  fifty-six  young 
clams.  The  largest  clam  was 
about  the  length  of  one  arm 
of  the  starfish,  the  smallest  about  ten  millimeters  in  length.  In  six 
days  every  clam  in  the  aquarium  was  devoured.  The  method  of 
capturing  and  killing  their  prey  shows  that  they  wrap  themselves  around 
the  valves  of  the  mollusk  and  actually  puU  apart  the  valves  by  means 
of  their  tube  feet,  some  of  which  are  attached  to  one  valve  and  some 
to  the  other  of  their  victim.  Once  the  soft  part  of  the  mollusk  is 
exposed,  the  stomach  envelops  it,  and  it  is  rapidly  digested  and  changed 
to  a  fluid.  This  it  can  do  because  of  the  five  large  digestive  glands 
which  occupy  a  large  part  of  each  ray,  and  which  pour  their  digestive 
fluids  into  five  pouchlike  extensions  of  the  stomach  extending  into 
each  ray. 

Hundreds  of  thousands  of  dollars'  damage  is  done  annually  to  the 
oysters   in  Connecticut   alone  by  the  ravages  of  starfish.     During  the 


Ventral  or  under  surface  of  the  starfish.  The 
dark  circle  in  the  middle  is  the  mouth,  from 
which  radiate  the  five  ambulacral  grooves, 
each  filled  with  four  rows  of  tube  feet.  Photo- 
graph half  natural  size,  by  Davison. 


THE  MOLLUSKS  273 

summer  months  the  oyster  boats  are  to  be  found  at  work  raking  the  beds 
for  starfish,  which  are  collected  and  thrown  ashore  by  the  thousands. 

Classification  of  Mollusks 

Class  I.  Pelecypoda  (Lamellibranchiata).  Soft-bodied  unsegmented  animals  show- 
ing bilateral  symmetry.  Bivalve  shell,  platelike  gills.  Examples  :  clam  (Mya 
arenaria),   scallop   (pecten),   oyster    (Ostrea),   and    fresh-water   mussel   (Unto). 

Class  II.  Gastropoda.  Soft  bodies  asymmetrical ;  univalve  shell  or  shell  absent. 
Some  forms  breathe  by  gills,  others  by  lunglike  sacs.  Examples  *  pond  snail, 
land  snail  (Helix),  and  slug. 

Class  III.  Cephalopoda.  Bilaterally  symmetrical  mollusks  with  mouth  sur- 
rounded by  tentacles.  Shell  may  be  external  (nautilus),  internal  (squid),  or 
altogether  lacking  (octopus).     Examples:  squid,  octopus. 

Reference  Books 

elementary 

Sharpe,  A  Laboratory  Manual  for  the  Solution  of  Problems  in  Biology.    American 

Book  Company. 
Davison,  Practical  ZoOlogy,  pages  142-150.     American  Book  Company. 
HeUprin,  The  Animal  Life  of  our  Seashore.     J.  B.  Lippincott  Company. 
Jordan,  Kellogg,  and  Heath,  Animal  Studies.     D.  Appleton  and  Company. 
Morgan,  Animal  Sketches,  Chap.  XXI.     Longmans,  Green,  and  Company. 

ADVANCED 

Bulletin,  U.S.  Fish  Commission,  1889. 

Brooks,  The  Oyster.     Johns  Hopkins  Press. 

Cooke,  "The  Mollusca,"  Cambridge  Natural  History.     The  Macmillan  Company. 

Kellogg,  The  Life  History  of  the  Common  Clam.    Bulletin,  U.S.   Fish  Commission, 

Vol.  XIX,  page  193. 
Kellogg,  The  Shellfish  Industries.     Henry  Holt  and  Company. 
Parker,  Elementary  Biology.     The  Macmillan  Company. 
Parker  and  Haswell,  Textbook  of  Zoology.     The  Macmillan  Company. 


HUNT.  ES.  BIO. 18 


XXII.    THE  VERTEBRATE  ANIMALS 


Increasing  Complexity  of  Structure  and  of  Habits  in  Plants  and 
Animals.  —  In  our  study  of  biology  so  far  we  have  attempted  to 
get  some  notion  of  the  various  factors  which  act  upon  and  interact 
with  living  things.  We  have  learned  something  about  the  various 
physiological  processes  of  plants  and  animals,  and  have  found  them 
to  be  in  many  respects  identical.  We  have  examined  a  number 
of  forms  of  plants  and  have  found  all  grades  of  complexity,  from 
the  one-celled  plant,  bacterium  or  pleurococcus,  to  the  complicated 
flowering  plants  of  considerable  size  and  with  many  organs.  So 
in  animal  life  the  forms  we  may  have  studied,  from  the  Protozoa 
upward,  there  is  constant  change,  and  the  change  is  toward  greater 
complexity  of  structure  and  functions.  A  worm  is  simpler  in 
structure  than  an  insect,  and  in  many  ways,  especially  by  its  actions, 
shows  that  it  is  not  so  high  in  the  scale  of  life  as  its  more  lively 
neighbor. 

We  are  already  awake  to  the  fact  that  we,  as  living  creatures, 
are  better  equipped  in  the  battle  for  life  than  our  more  lowly  neigh- 
bors, for  we  are  thinking 
creatures,  and  can  change 
our  surroundings  at  will, 
while  the  lower  forms  of 
animals  are  largely  con- 
trolled by  stimuli  which 
come  from  without;  tem- 
perature, moisture,  light, 
the  presence  or  absence  of 
food,  —  all  these  result  in 
movement  and  other  re- 
actions. 

In  structure  we  also  differ.  Particularly  is  this  difference  seen 
in  the  skeleton.     We  call  ourselves  vertebrates,  because  we  have  a 

274 


Cross  section  through  (/)  an  invertebrate  ani- 
mal and  (F)  a  vertebrate  animal:  a,  food  tube; 
6,  heart;  c,  vertebrate  column;  n,  central  nerv- 
ous system. 


THE  VERTEBRATE  ANIMALS 


275 


bony  vertebral  column,  made  up  of  pieces  of  bone  joined  one 
to  another,  forming  a  flexible  yet  strong  support  for  the  muscles 
and  protecting  the  delicate  central  nervous  system.  This  kind 
of  an  endoskeleton,  or  inside  skeleton,  is  possessed  by  fishes,  frogs, 
turtles  or  snakes,  and  birds,  and  by  mammals,  such  as  the  dog, 
cat,  and  man.  All  such  animals  are  called  vertebrates.  We 
are  now  to  take  up  the  study  of  some  types  of  various  kinds  of 
vertebrates,  with  the  view  to  a  better  understanding  of  man. 

Fishes 
Problem  XXXIV,    A  study  of  how  a  fish  is  fitted  for  tlie  life 
it  leads.    (^Laboratory  Manual,  Prob,  XXXIV.) 

The  Body.  —  One  of  our  common  fresh-water  fish  is  the  bream, 
or  golden  shiner.  The  body  of  the  bream  runs  insensibly  into 
the  head,  the  neck  being  absent.  The  long,  narrow  body  with  its 
smooth  surface  fits  the  fish  admirably  for  its  life  in  the  water. 
Certain  cells  in  the  skin  secrete  mucus  or  slime,  another  adapta- 
tion. The  position  of  the  scales,  overlapping  in  a  backward 
direction,  is  yet  another  adaptation  which  aids  in  passing  through 


The  fins  of  a  fish  :   A,  dorsal ;   B,  caudal ;    C,  anal ;    Z>,  pelvic  ;    E,  pectoral. 


the  water.     Its   color,  olive  above  and   bright   silver   and  gold 
below,  is  also  protective.     Can  you  see  how? 

The  Appendages  and  their  Uses.  —  The  appendages  of  the  fish 
consist  of  paired  and  unpaired  fins.  The  paired  fins  are  four  in 
number,  and  are  believed  to  correspond  in  position  and  structure 


276  THE  VERTEBRATE  ANIMALS 

with  the  paired  limbs  of  a  man.  Note  the  Figure  on  page  326 
and  locate  the  paired  pectoral  and  pelvic  fins.  (These  are  so  called 
because  they  are  attached  to  the  bones  forming  the  pectoral  and 
pelvic  girdles.  See  page  426.)  Find,  by  comparison  with  the 
Figure,  the  dorsal,  anal,  and  caudal  fins.  How  many  unpaired 
fins  are  there? 

The  flattened,  muscular  body  of  the  fish,  tapering  toward  the 
caudal  fin,  is  moved  from  side  to  side  with  an  xmdulating  motion 
which  results  in  the  movement  forward  of  the  fish.  This  movement 
is  almost  identical  with  that  of  an  oar  in  sculling  a  boat.  Turning 
movements  are  brought  about  by  use  of  the  lateral  fins  in  much 
the  same  way  as  a  boat  is  turned.  We  notice  the  dorsal  and  other 
single  fins  are  evidently  useful  as  balancing  and  steering  organs. 

The  Senses.  —  The  position  of  the  eyes  at  the  side  of  the  head 
is  an  evident  advantage  to  the  fish.  Why?  The  eye  is  globular 
in  shape.  Such  an  eye  has  been  found  to  be  very  nearsighted. 
Thus  it  is  unlikely  that  a  fish  is  able  to  perceive  objects  at  any  great 
distance  from  it.  The  eyes  are  unprotected  by  eyelids,  but  the 
tough  outer  covering  and  their  position  afford  some  protection. 

Feeding  experiments  with  fishes  show  that  a  fish  becomes  aware 
of  the  presence  of  food  by  smelling  it  as  well  as  by  seeing  it.  The 
nostrils  of  a  fish  can  be  proved  to  end  in  little  pits,  one  under  each 
nostril  hole.  Thus  they  differ  from  our  own,  which  are  connected 
with  the  mouth  cavity.  In  the  catfish,  for  example,  the  barbels, 
or  horns,  receive  sensations  of  smell  and  taste.  The  sense  of  per- 
ceiving odor  is  not  as  we  understand  the  sense  of  smell,  for  a  fish 
perceives  only  substances  that  are  dissolved  in  the  water  in  which  it 
lives.  The  senses  of  taste  and  touch  appear  to  be  less  developed 
than  the  other  senses. 

Along  each  side  of  most  fishes  is  a  line  of  tiny  pits,  provided  with 
sense  organs  and  connected  with  the  central  nervous  system  of  the 
fish.  This  area,  called  the  lateral  line,  is  believed  to  be  sensitive 
to  mechanical  stimuli  of  certain  sorts.  The  "  ear  "  of  the  fish  is 
under  the  skin  and  serves  partly  as  a  balancing  organ. 

A  fish  must  go  after  its  food  and  seize  it,  but  has  no  structures 
for  grasping  except  the  teeth.  Consequently  we  find  the  teeth 
small,  sharp,  and  numerous,  well  adapted  for  holding  hving  prey. 
The  tongue  in  most  fishes  is  wanting  or  very  slightly  developed. 


THE   VERTEBRATE  ANIMALS  277 

Breathing.  —  A  fish,  when  swimming  quietly  or  when  at  rest, 
seems  to  be  biting  when  no  food  is  present.  A  reason  for  this  act 
is  to  ))e  seen  when  we  introduce  a  Httle  finely  powdered  carmine 
into  the  water  near  the  head  of  the  fish.  It  will  be  found  that  a 
current  of  water  enters  the  mouth  at  each  of  these  biting  move- 
ments and  passes  out  through  two  slits  found  on  each  side  of  the 
head  of  the  fish.  Investigation  shows  us  that  under  the  broad,  flat 
plate,  or  operculum,  forming  each  side  of  the  head,  lie  several  long, 
feathery,  red  structures,  the  gills. 

Gills.  —  If  we  examine  the  gills  of  any  large  fish,  we  find  that  a 
single  gill  is  held  in  place  by  a  bony  arch,  made  of  several  pieces 

of  bone  which  are  hinged  in  such 
a  way  as  to  give  great  flexibility 
to  the  gill  arch,  as  the  support 
is  called.  Covering  the  bony 
framework,  and  extending  from 
it,  are  numerous  delicate  fila- 
ments  of   flesh,    covered    with 

The  head  of  a  fish,  with   the  operculum  j   r      x  u 

cut  away  to  show  the  gUIs.  ^   ^^^y  delicate  membrane  or 

skin.  Into  each  of  these  fila- 
ments pass  two  blood  vessels;  in  one  blood  flows  downward  and 
in  the  other  upward.  Blood  reaches  the  gills  and  is  carried  away 
from  these  organs  l)y  means  of  two  large  vessels  which  pass  along 
the  bony  arch  previously  mentioned.  In  the  gill  filament  the  blood 
comes  into  contact  with  the  free  oxygen  of  the  water  bathing  the 
gills.  An  exchange  of  gases  through  the  walls  of  the  gill  filaments  re- 
sults in  the  loss  of  carbon  dioxide  and  a  gain  of  oxygen  by  the  blood. 
Gill  Rakers.  —  If  we  open  wide  the  mouth  of  any  large  fish  and 
look  inward,  we  find  that  the  mouth  cavity  leads  to  a  funnel-like 
opening,  the  gullet.  On  each  side  of  the  gullet  we  can  see  the  gill 
arches,  guarded  on  the  inner  side  by  a  series  of  sharp-pointed  struc- 
tures, the  gill  rakers.  In  some  fishes  in  which  the  teeth  are  not 
well  developed,  there  seems  to  be  a  greater  development  of  the 
gill  rakers,  which  in  this  case  are  used  to  strain  out  small  organisms 
from  the  water  which  passes  over  the  gills.  Many  fishes  make 
such  use  of  the  gill  rakers.  Such  are  the  shad  and  menhaden, 
which  feed  almost  entirely  on  plankton,  a  name  given  to  the  small 
plants  and  animals  found  by  millions  in  the  water. 


278 


THE  VERTEBRATE  ANIMALS 


Digestive  System.  —  The  gullet  leads  directly  into  a  baglike  stomach. 
There  are  no  sahvary  glands  in  the  fishes.  There  is,  however,  a  large 
liver,  which  appears  to  be  used  as  a  digestive  gland.  This  organ,  because 
of  the  oil  it  contains,  is  in  some  fishes,  as  the  cod,  of  considerable  economic 
importance.  Many  fishes  have  outgrowths  like  a  series  of  pockets  from 
the  intestine.  These  structures,  called  the  pyloric  cosca,  are  believed  to 
secrete  a  digestive  fluid.  The  intestine  ends  at  the  vent,  which  is  usually 
located  on  the  ventral  side  of  the  fish,  immediately  in  front  of  the  anal  fin. 


Anatomy  of  the  carp  :  br,  branehi:Te,  or  gills ;    c,  heart 
bladder;   d,  intestine. 


/,  liver ;    vn,    swimming 


Swim  Bladder.  —  An  organ  of  unusual  significance,  called  the  swim 
bladder,  occupies  the  region  just  dorsal  to  the  food  tube.  In  young  fishes 
of  many  species  this  is  connected  by  a  tube  with  the  anterior  end  of  the 
digestive  tract.  In  some  forms  this  tube  persists  throughout  life,  but 
in  other  fish  it  becomes  closed,  a  thin,  fibrous  cord  taking  its  place. 
The  swim  bladder  aids  in  giving  the  fish  nearly  the  same  weight  as  the 
water  it  displaces,  thus  buoying  it  up.  The  walls  of  the  organ  are  richly 
supplied  with  blood  vessels,  and  it  thus  undoubtedly  serves  as  an  organ 
for  supplying  oxygen  to  the  blood  when  all  other  sources  fail.  In  some 
fish  (the  dipnoi,  p.  284)  it  has  come  to  be  used  as  a  lung. 

Circulation  of  the  Blood.  —  In  the  vertebrate  animals  the  blood  is 
said  to  circulate  in  the  body,  because  it  passes  through  a  more  or  less  closed 
system  of  tubes  in  its  course  around  the  body.  In  the  fishes  the  heart  is 
a  two-chambered  muscular  organ,  a  thin-walled  auricle,  the  receiving 
chamber,  leading  into  a  thick-walled  muscular  ventricle  from  which  the 
blood  is  forced  out.  The  blood  is  pumped  from  the  heart  to  the  gills ; 
there  it  loses  some  of  its  carbon  dioxide ;   it  then  passes  on  to  other  parts 


THE  VERTEBRATE  ANIMALS 


279 


of  the  body,  eventually  breaking  up  into  very  tiny  tubes  called  capillaries. 
From  the  capillaries  the  blood  returns,  in  tubes  of  gradually  increasing 
diameter,  toward  the  heart  again.  During  its  course  some  of  the  blood 
passes  through  the  kidnej's  and  is  there  relieved  of  part  of  its  nitroge- 
nous waste.     (See  Chapter  XXVII.) 

Circulation  of  blood  in  the  body  of  the  fish  *'-. 

is  rather  slow.  The  temperature  of  the  blood 
being  nearly  that  of  the  surrounding  media  in 
which  the  fish  hves,  the  animal  has  incorrectly 
been  given  the  terra  "cold-blooded." 

Nervous  System.  — As  in  all  other  vertebrate 
animals,  the  l)rain  and  spinal  cord  of  the  fish  are 
partially  inclosed  in  a  series  of  bony  structures 
called  vertebra;.  The  central  nervous  system  con- 
sists of  a  brain,  with  nerves  leading  to  the  oi^ans 
of  sight,  taste,  smell,  the  ear,  and  to  such  parts  of 
the  body  as  possess  the  sense  of  touch ;  a  spinal 
cord;  and  spinal  nerves.  Nerve  cells  located 
near  the  outside  of  the  body  send  in  messages 
to  the  central  system,  which  are  there  received 
as  sensations.  Cells  of  the  central  nervous  sys- 
tem, in  turn,  send  out  messages  which  result  in 
the  movement  of  muscles. 

Skeleton.  —  In  the  vertebrates,  of  which  the 
bony  fish  is  an  example,  the  skeleton  is  under 
the  skin,  and  is  hence  called  an  endoskeleton. 
It  consists  of  a  bony  framework,  the  vertebral 
column,  and  certain  attached  bones,  the  ribs, 
with  other  spiny  bones  to  which  the  unpaired  fins 

are  attached.  The  paired  fins  are  attached  to  the  spinal  column  by  two 
collections  of  bones,  known  respectively  as  the  pectoral  and  pelvic  girdles. 
The  bones  serve  in  the  fish  for  the  attachment  of  powerful  muscles,  by 
means  of  which  locomotion  is  accomplished.  In  most  fishes,  the  exo- 
skeleton,  too,  is  well  develoi)ed,  modifications  appearing  from  scales  to 
complete  armor. 


Plan  of  circulation  in  fishes : 
a,  auricle  ;  b,  ventricle  ;  c, 
branchial  artery ;  e,  bran- 
chial veins,  bringing  blood 
from  the  gills,  d,  and  unit- 
ing in  the  aorta,  /;  g,  vena 
cava,  returning  blood  to 
heart. 


Prohlem  XXXV  (Ojttional).  A  study  of  sortie  of  the  relations 
of  fislies  to  tJieir  food  supply.  (^Laboratory  Manual,  Prob. 
XXXV.) 


Food  of  Fishes.  —  We  have  already  seen  that  in  a  balanced 
aquarium  tlie  l)alance  of  food  was  preserved  by  the  plants,  which 
furnished  food  for  the  tiny  animals  or  were  eaten  by  larger  ones,  — 
for  example,  snails  or  fish.     The  smaller  animals  in  turn  became 


280  THE  VERTEBRATE  ANIMALS 

food  of  larger  ones.  The  nitrogen  balance  was  maintained  through 
the  excretions  of  the  animals  and  their  death  and  decay. 

The  marine  world  is  a  great  balanced  aquarium.  The  upper 
layer  of  water  is  crowded  with  all  kinds  of  little  organisms,  both 
plant  and  animal.  Some  of  these  are  microscopic  in  size;  others, 
as  the  tiny  crustaceans,  are  visible  to  the  eye.  On  these  little 
organisms  some  fish  feed  entirely,  others  in  part.  Such  are  the 
menhaden  ^  (bony,  bunker,  mossbunker  of  our  coast),  the  shad, 
and  others.  Other  fishes  are  bottom  feeders,  as  the  blackfish  and 
the  sea  bass,  living  almost  entirely  upon  mollusks  and  crusta- 
ceans. Still  others  are  hunters,  feeding  upon  smaller  species  of 
fish  or  even  upon  their  weaker  brothers.  Such  are  the  bluefish, 
squeteague  or  weakfish,  and  others. 

What  is  true  of  salt-water  fish  is  equally  true  of  those  inhabiting 
our  fresh-water  streams  and  lakes.  It  is  one  of  the  greatest  prob- 
lems of  our  Bureau  of  Fisheries  to  discover  this  relation  of  various 
fishes  to  their  food  supplies  so  as  to  aid  in  the  conservation  and 
balance  of  life  in  our  lakes,  rivers,  and  seas. 

The  Egg-laying  Habits  of  the  Bony  Fishes.  —  The  eggs  of  most 
bony  fishes  are  laid  in  great  numbers  at  the  time  of  spawning. 
This  number  varies  from  a  few  thousand  in  the  trout  to  many 
hundreds  of  thousands  in  the  shad  and  several  millions  in  the  cod. 
The  time  of  egg-laying  is  usually  spring  or  early  summer.  At  the 
time  of  spawning  the  male  usually  deposits  milt,  consisting  of  mil- 
lions of  sperm  cells,  in  the  water  just  over  the  eggs,  thus  accomplish- 
ing fertihzation.  Some  fishes,  as  sticklebacks,  sunfish,  toadfish,  etc., 
make  nests,  but  usually  the  eggs  are  left  to  develop  by  themselves, 
sometimes  attached  to  some  submerged  object,  but  more  frequently 
free  in  the  water.  In  some  eggs  a  tiny  oil  drop  buoys  up  the  egg 
to  the  surface,  where  the  heat  of  the  sun  aids  development.  They 
are  exposed  to  many  dangers,  and  both  eggs  and  developing  fish 
are  eaten,  not  only  by  birds,  fish  of  other  species,  and  other  water 
inhabitants,  but  also  by  their  own  relatives  and  even  parents. 
Consequently  a  very  small  percentage  of  eggs  ever  reach  maturity. 

*  It  has  been  discovered  by  Professor  Mead  of  Brown  University  that  the  in- 
crease in  starfish  along  certain  parts  of  the  New  England  coast  was  in  part  due 
to  overfishing  of  menhaden,  which  at  certain  times  in  the  year  feed  ahnost  entirely 
on  the  young  starfish. 


THE   VERTEBRATE  ANIMALS 


281 


The  Relation  of  the  Spawning  Habits  to  Economic  Importance 
of  Fish.  —  The  spawning  habits  of  fish  are  of  great  importance  to  us 
because  of  the  economic  value  of  fish  to  mankind,  not  only  directly 
as  a  food,  but  indirectly  as  food  for  other  animals  in  turn  valuable 
to  man.  Many  of  our  most  desirable  food  fishes,  notably  the 
salmon,  shad,  sturgeon,  and  smelt,  pass  up  rivers  from  the  ocean 

to  deposit  their  eggs, 
swimming  against 
strong  currents  much 
of  the  way,  some  spe- 
cies leaping  rapids  and 
falls,  in  order  to  de- 
l)osit    their    eggs    in 


Salmon  leaping  a  fall  on  their  way  to  their 
spawning  beds.  Photographed  by  Dr.  John 
A.  Sampson. 


suitable  localities,  where 
the  conditions  of  water 
and  food  are  requisite, 
and  the  water  shallow 
enough  to  allow  the  sun's 
rays  to  warm  the  water 
sufficiently  to  cause  the 
eggs  to  develop.  The 
Chinook  salmon  of  the  Pacific  coast,  the  salmon  used  in  the  Western 
canning  industry,  travels  over  a  thousand  miles  up  the  Columbia 
and  other  rivers,  where  it  spawns.  The  salmon  begin  to  pass  up  the 
rivers  in  early  spring,  and  reach  the  spawning  beds,  shallow  de- 
posits of  gravel  in  cool  mountain  streams,  before  late  summer. 
Here  the  fish,  both  males  and  females,  remain  until  the  temperature 
of  the  water  falls  to  about  54°  Fahrenheit.  The  eggs  and  milt  are 
then  deposited,  and  the  old  fish  die,  leaving  the  eggs  to  be  hatched 
out  later  by  the  heat  of  the  sun's  rays. 


282 


THE   VERTEBRATE  ANIMALS 


This  instinct  of  this  fish  and  other  species  to  go  into  shallow  rivers 
to  deposit  their  eggs  has  been  made  use  of  by  man.  At  the  time 
of  the  spawning  migration  the  salmon  are  taken  in  vast  numbers. 
The  salmon  fisheries  net  over  $16,000,000  annually,  the  shad  at 


least  $1,500,000,  the  smelt  fishery  nearly  $150,000  more.  The 
total  annual  value  of  the  fisheries  of  the  United  States  is  over 
$50,000,000. 

Migration  of  Fishes. —  Some  fishes  change  their  habitat  at  dif- 
ferent times  during  the  year,  moving  in  vast  schools  northward 
in  summer  and  southward  in  the  winter.  In  a  general  way  such 
migrations  follow  the  coast  lines.  Examples  of  such  migratory 
fish  are  the  cod,  menhaden,  herring,  and  bluefish.  The  migra- 
tions are  due  to  temperature  changes,  to  the  seeking  after  food, 


Fisheries— Percentage  Product 

ifi 40 5^ 6,0 TO 


ME 


_e£_ 


United  States     Gt.Brit.  &  Ir. 


Can.  & 
Newf. 


Japan     Russia  France  ^'^  ,        Rest  of  World 


and  to  the  spawning  instinct.  Some  fish  migrate  to  shallower 
water  in  the  summer  and  to  deeper  water  in  the  winter ;  here  the 
reason  for  the  migration  is  doubtless  the  change  in  temperature. 

The  herring  fisheries  have  always  been  a  source  of  wealth  to 
the  inhabitants  of  northern  Europe.  The  banks  and  shallows  of 
the  coast  of  Newfoundland  were  undoubtedly  known  to  the  Norse-, 
men  long  before  the  discovery  of  this  country  by  Columbus. 


THE  VERTEBRATE  ANIMALS  283 

rrobleni  XXXVl  (Oj}tional).  The  artificial  propagation  of 
fislies.    {Laboratory  ManicaJ,  Froh.  XX'X'VI.) 

The  Work  of  National  and  State  Governments  in  protecting  and 
propagating  Food  Fishes.  —  But  the  profits  from  the  fisheries 
are  steadily  decreasing  because  of  the  yearly  destruction  of  untold 
millions  of  eggs  which  might  develop  into  adult  fish. 

Fortunately,  the  government  through  the  Bureau  of  Fisheries, 
and  various  states  by  wise  protective  laws  and  by  artificial  prop- 
agation of  fishes,  are  beginning  to  turn  the  tide.  Certain  days  of 
the  week  the  salmon  are  allowed  to  pass  up  the  Columbia  unmo- 
lested. Closed  breeding  seasons  protect  our  trout,  bass,  and  other 
game  fish,  and  also  prohibit  the  catching  of  fish  under  a  certain 
size.  Many  fish  hatcheries,  both  government  and  state,  are  en- 
gaged in  artificially  fertilizing  millions  of  fish  eggs  of  various  species 
and  protecting  the  young  fry  until  they  can  be  placed  in  ponds  or 
streams  at  a  size  when  they  can  take  care  of  themselves.  This 
artificial  fertiUzation  is  usually  accomplished  by  first  squeezing  out 
the  ripe  eggs  from  a  female  into  a  pan  of  water;  in  a  similar  manner 
the  milt  or  sperm  cells  are  obtained,  and  poured  over  the  eggs.  The 
fertilized  eggs  are  carefully  protected,  and,  after  hatching,  the 
young  fry  are  kept  in  ideal  conditions  until  later  they  are  shipped, 
sometimes  thousands  of  miles,  to  their  new  home. 

State  and  government  interposition,  however,  is  in  many  cases 
coming  too  late,  for  at  the  present  rate  of  destruction  many  of  our 
most  desirable  food  fishes  will  soon  be  extinct.  The  sturgeon,  the 
eggs  of  which  are  used  in  the  manufacture  of  the  delicacy  known 
as  caviare,  is  an  example  of  a  fish  that  is  almost  extinct  in  this  part 
of  the  world.  The  shad  is  found  in  fewer  numbers  each  year, 
and  in  fewer  rivers  as  well.  The  salmon  will  undoubtedly  soon 
meet  the  fate  of  other  fishes  which  are  taken  at  the  spawning 
season,  unless  conservation  of  a  radical  sort  takes  place. 

Classification  of  Fishes.  —  The  animals  we  recognize  as  fishes  are 
grouped  by  naturalists  into  four  groups :  — 

1.  The  Elasmobranchs.  —  These  fishes  have  a  skeleton  formed  of 
cartilage  which  has  not  become  hardened  with  lime.  The  gills  com- 
municate with  the  surface  of  the  body  by  separate  openings  instead  of 
having  an  operculum.     The  skin  is  rough  and  the  eggs  few  in  number. 


284 


THE  VERTEBRATE  ANIMALS 


Sand  shark,  an  elasmobranch.     Note  the  sUts  leading  from  the  gills.     From  photo- 
graph loaned  by  the  American  Museum  of  Natural  History. 


Sturgeon  {Acipenser  sturio),  a  ganoid  fish. 


'M: 


In  some  members  of  this  group  the  young  are  born  alive.     Sharks,  rays, 
and  skates  are  elasmobranchs. 

2.  Ganoids.  —  The  bodies  of  these  are  ganoids  protected  by  a  series  of 
platelike  scales  of  considerable  strength.  These  fishes  are  the  only  rem- 
nant of  what  once  was  the  most  powerful  group  of  animals  on  the  earth,  the 

great  armored  fishes  of  the  Devonian 
age.     The  gar  pike  is  an  example. 

3.  The  Teleosts,  or  Bony  Fishes.  — 
They  compose  95  per  cent  of  all  living 
fishes.  In  this  group  the  skeleton  is 
bony,  the  gills  are  protected  by  an 
operculum,  and  the  eggs  are  numerous. 
Most  of  our  common  food  fishes  belong 
to  this  class. 

4.  The  Dipnoi,  or  Lung  Fishes.  —  This  is  a  very  small  group,  in  many 
respects  more  Uke  amphibians  than  fishes,  the  swim  bladder  being  used 
as  a  lung.  They  live  in  tropical  Africa,  South  America,  and  Australia, 
inhabiting  the  rivers  and  lakes  there.  They  withstand  drying  up  in  the 
mud  during  the  dry  season,  lying  dormant  for  long  periods  of  time  in  a 
ball  of  mud  and  waking  to  active  life  again  when  the  mud  coat  is  removed 
by  immersion  in  water. 


A  bony  fish. 


THE  VERTEBRATE  ANIMALS 


285 


Reference  Books 
elementary 

Sharpe,  A  Laboratory  Manual.    American  Book  Company. 
Davison,  Practical  Zoology,  pages  185-199.     American  Book  Company. 
Herrick,  Textbook  in  General  Zoology,  Chap.  XIX.     American  Book  Company. 
Jordan,  Kellogg,  and  Heath,  Animal  Studies,  XIV.    D.  Appleton  and  Company. 

ADVANCED 

Jordan  and  Evermann,  American  Food  and  Gam^  Fishes.     Doubleday,  Page,  and 

Company. 
Jordan,  Fishes.     Henry  Holt  and  Company. 

Kingsley,  Textbook  of  Vertebrate  Zoology.     Henry  Holt  and  Company. 
Riverside  Natural  History.     Houghton,  Mifflin,  and  Company. 


Amphibia.     The   Frog 

Problem  XXXVII.    Some  adaptations   in    a   living  frog. 
{Laboratory  Manual,  Prob.  XXX VII.) 

Adaptations  for  Life.  —  The  most  common  frog  in  the  eastern 
part  of  the  United  States  is  the  leopard  frog.  It  is  recognized  by 
its  greenish  brown  body  with  dark  spots,  each  spot  being  outlined 
in  a  Hghter  colored  background.  In  spite  of  the  apparent  lack  of 
harmony  with  their  sur- 
roundings, their  color,  on  the 
contrary,  appears  to  give 
almost  perfect  protection. 
In  some  species  of  frogs  the 
color  of  the  skin  changes 
with  the  surroundings  of  the 
frog,  another  means  of  pro- 
tection. 

Adaptations  for  life  in  the 
water    are    numerous.     The 
ovoid  body,  the  head  merg- 
ing into  the  trunk,  the  slimy  ^^^^  l^^      .  ^^^^  ^ 
covering  (for  the  frog  is  pro- 
vided, like  the  fish,  with  mucus  cells  in  the  skin),  and  the  power- 
ful legs  with  webbed  feet,  are  all  evidences  of  the  Ufe  which  the 
frog  leads. 


286        THE  VERTEBRATE  ANIMALS 

Locomotion.  —  You  will  notice  that  the  appendages  have  the 
same  general  position  on  the  body  and  same  number  of  parts  as  do 
your  own  (upper  arm,  forearm,  and  hand ;  thigh,  shank,  and  foot, 
the  latter  much  longer  relatively  than  your  own).  Note  that  while 
the  hand  has  four  fingers,  the  foot  has  five  toes,  the  latter  connected 
by  a  web.  In  swimming  the  frog  uses  the  stroke  we  all  aim  to 
make  when  we  are  learning  to  swim.  Most  of  the  energy  is  liber- 
ated from  the  powerful  backward  push  of  the  hind  legs,  which  in  a 
resting  position  are  held  doubled  up  close  to  the  body.  On  land, 
locomotion  may  be  by  hopping  or  crawling. 

Sense  Organs.  —  The  frog  is  well  provided  with  sense  organs. 
The  eyes  are  large,  globular,  and  placed  at  the  side  of  the  head. 
When  they  are  closed,  a  delicate  fold,  called  the  nictitating  mem" 
hrane  (or  third  eyelid),  is  drawn  over  each  eye.  Frogs  probably 
see  best  moving  objects  at  a  few  feet  from  them.  Their  vision  is 
much  keener  than  that  of  the  fish.  The  external  ear  (tympanum) 
is  located  just  behind  the  eye  on  the  side  of  the  body.  Frogs  hear 
sounds  and  distinguish  various  calls  of  their  own  kind,  as  is  proved 
by  the  fact  that  frogs  recognize  the  warning  notes  of  their  mates 
when  any  one  is  approaching.  The  inner  ear  also  has  to  do  with 
balancing  the  body  as  it  has  in  fishes  and  other  vertebrates.  Taste 
and  smell  are  probably  .not  strong  sensations  in  a  frog  or  toad. 
They  bite  at  moving  objects  of  almost  any  kind  when  hungry. 
Experience  has  taught  these  animals  that  moving  things,  insects, 
worms,  and  the  like,  make  good  food.  These  they  swallow  whole, 
the  tiny  teeth  being  used  to  hold  the  food.  Touch  is  a  well- 
developed  sense.  They  also  respond  to  changes  in  temperature 
under  water,  remaining  there  in  a  dormant  state  for  the  winter 
when  the  temperature  of  the  air  becomes  colder  than  that  of  the 
water. 

Breathing.  —  The  frog  breathes  by  raising  and  lowering  the 
floor  of  the  mouth,  pulling  in  air  through  the  two  nostril  holes. 
Then  the  little  flaps  over  the  holes  are  closed,  and  the  frog  swallows 
this  air,  thus  forcing  it  down  into  the  baglike  lungs.  The  skin 
is  provided  with  many  tiny  blood  vessels,  and  in  winter,  while  the 
frogs  are  dormant  at  the  bottom  of  the  ponds,  it  serves  as  the 
only  organ  of  respiration. 

Although  we  shall  take  up  the  study  of  the  internal  structure  of 


THE  VERTEBRATE  ANIMALS 


287 


the  frog  more  in  detail  when  we  discuss  the  structure  and  uses  of 
the  parts  of  the  bociy  in  man,  we  may  now  learn  something  of  the 
position  and  use  of  some  of  the  structures  found  within  the  body 
cavity. 

The  Food  Tube  and  its  Glands. —  The  mouth  leads  like  a  funnel 
into  a  short  tube,  the  gullet.  On  the  lower  floor  of  the  mouth  can 
be  seen  the  slitlike  glottis  leading  to  the  lungs.  The  gullet  widens 
almost  at  once  into  a  long  stomach,  which  in  turn  leads  into  a  much- 


BaMone_Omiuct     Spinal  cord_^^^g^^^ 


Tongue 


Glottis 


Liver 
Pancreas 

Diagram  of  the  internal  anatomy  of  a  frog. 

coiled  intestine.  This  widens  abruptly  at  the  lower  end  to  form 
the  large  intestine.  This  in  turn  leads  into  the  cloaca  (Latin, 
sewer)  into  which  open  the  kidneys,  urinary  bladder,  and  repro- 
ductive organs  {ovaries  or  spermaries).  Several  glands,  the 
function  of  which  is  to  produce  digestive  fluids,  open  into  the 
food  tube.  These  digestive  fluids,  by  means  of  the  ferments  or 
enzymes  contained  in  them,  change  insoluble  food  materials  into 
a  soluble  form.  This  allows  of  the  absorption  of  food  material 
through  the  walls  of  the  food  tube  into  the  blood.  The  glands 
(having  the  same  names  and  uses  as  those  in  man)  are  the  salivary 
glands,  which  pour  their  juices  into  the  mouth,  the  gastric  glands 
in  the  walls  of  the  stomach,  and  the  liver  and  pancreas,  which 
open  into  the  intestine.     (See  Digestion,  pages  352-365.) 

Circulation.  —  The  frog  has  a  well-developed  heart,  composed  of  a 
thick-walled  muscular  ventricle  and  two  thin-walled  auricles.  The  heart 
pumps  the  blood  through  a  system  of  closed  tubes  to  all  parts  of  the  body. 
Blood  enters  the  right  auricle  from  all  parts  of  the  body ;   it  then  con- 


288        THE  VERTEBRATE  ANIMALS 

tains  considerable  carbon  dioxide ;  the  blood  entering  the  left  auricle  comes 
from  the  lungs,  hence  it  contains  a  considerable  amount  of  oxygen.  Blood 
leaves  the  heart  through  the  ventricle,  which  thus  pumps  blood  contain- 
ing much  and  little  oxygen.  Before  the  blood  from  the  tissues  and  lungs 
has  time  to  mix,  however,  it  leaves  the  ventricle  and  by  a  delicate  adjust- 
ment in  the  vessels  leaving  the  heart  most  of  the  blood  containing  much 
oxygen  is  passed  to  all  the  various  organs  of  the  body,  while  the  blood 
deficient  in  oxygen,  but  containing  a  large  amount  of  carbon  dioxide,  is 
pumped  to  the  lungs,  where  an  exchange  of  oxygen  and  carbon  dioxide 
takes  place  by  osmosis. 

In  the  tissues  of  the  body  wherever  work  is  done  the  process  of 
burning  or  oxidation  must  take  place,  for  by  such  means  only  is  the 
energy  necessary  to  do  the  work  released.  Food  in  the  blood  is  taken  to 
the  muscle  cells  or  other  cells  of  the  body  and  there  oxidized.  The  prod- 
ucts of  the  burning  —  carbon  dioxide  —  and  any  other  organic  wastes 
given  off  from  the  tissues  must  be  eliminated  from  the  body.  As  we 
know,  the  carbon  dioxide  passes  off  through  the  lungs  and  to  some  extent 
through  the  skin  of  the  frog,  while  the  nitrogenous  wastes,  poisons  which 
must  be  taken  from  the  blood,  are  eliminated  from  it  in  the  kidneys. 
Thus  wastes  are  passed  off  from  the  body. 

Problem  XXXVIII.    The  development  of  a  frog.    {Laboratory 
Manual,  Proh.  XXXVI.) 
{a)  Conditions  favorable. 

(b)  Metamorphosis. 

(c)  Development  of  a  toad  {optional). 

Field  and  Home  Work.  —  During  the  first  warm  days  in  March  or 
April,  look  for  gelatinous  masses  of  frogs'  eggs  attached  to  sticks  or  water 
weed  in  shallow  ponds.  Collect  some  and  try  to  hatch  them  out  in  a 
shallow  dish  in  the  window  at  home.  Make  experiments  to  learn  whether 
temperature  affects  the  development  of  the  egg  in  any  way.  Place  eggs 
in  dishes  of  water  in  a  warm  room  and  in  a  cold  room,  also  some  in  the 
ice  box.  Make  observations  for  several  weeks  as  to  rate  of  development 
of  each  lot  of  eggs.  Also  try  placing  a  large  number  of  eggs  in  one  dish, 
thus  cutting  down  the  supply  of  available  oxygen,  and  in  another  dish 
near  by,  under  the  same  conditions  of  light  and  heat,  place  a  few  eggs. 
Do  both  batches  of  eggs  develop  with  the  same  rapidity?  In  all  these 
experiments  be  sure  to  use  eggs  from  the  same  egg  mass,  so  as  to  make  sure 
that  all  are  of  the  same  age. 

Development. — The  eggs  of  the  leopard  frog  are  laid  in  shallow 
water  in  the  early  spring.  Masses  of  several  hundred,  which  may- 
be found  attached  to  twigs  or  other  supports  under  water,  are  de- 


THE  VERTEBRATE  ANIMALS 


289 


posited  at  a  single  laying.  Immediately  before  leaving  the  body 
of  the  female  they  receive  a  coating  of  jellylike  material,  which 
swells  up  after  the  eggs  are  laid.  Thus  they  are  protected  from 
the  attack  of  fish  or  other  animals  which  might  use  them  as  food. 
The  upper  side  of  the  egg  is  dark,  the  light-colored  side  being 
weighted  down  with  a  supply  of  yolk  (food).  The  fertilized  egg 
soon  segments  (divides  into  many  cells),  and  in  a  few  days,  if  the 
weather  is  warm,  these  cells  have  each  grown  into  an  oblong  body 
which  shows  the  form  of  a 
tadpole.  Shortly  after  the 
tadpole  wriggles  out  of  the 
jelly hke  case  and  begins  life 
outside  the  egg.  At  first  it 
remains  attached  to  some 
water  weed  by  means  of  a 
pair  of  suckerlike  projec- 
tions; later  a  mouth  is 
formed  at  this  point,  and 
the  tadpole  begins  to  feed 
upon  alga?  or  other  tiny 
water  plants.  At  this  time, 
about  two  weeks  after  the 
eggs  were  laid,  gills  are  pres- 
ent on  the  outside  of  the 
body.  Soon  after,  the  ex- 
ternal gills  are  replaced  by 
gills  which  grow  out  under  a  fold  of  the  skin  which  forms  an 
operculum  somewhat  as  in  the  fish.  Water  reaches  the  gills 
through  the  mouth  and  passes  out  through  a  hole  on  the  left  side 
of  the  body.  As  the  tadpole  grows  larger,  legs  appear,  the  hind  legs 
first,  although  for  a  time  locomotion  is  performed  by  means  of  the 
tail.  In  the  leopard  frog  the  change  from  the  egg  to  adult  is  com- 
pleted in  one  summer.  In  late  July  or  early  August,  the  tadpole 
begins  to  eat  less,  the  tail  becomes  smaller  (being  absorbed  into 
other  parts  of  the  body),  and  before  long  the  transformation  from 
the  tadpole  to  the  young  frog  is  complete.  In  the  green  frog  and 
bullfrog  the  metamorphosis  is  not  completed  until  the  begin- 
ning of  the  second  siunmer.      The  large  tadpoles  of  such  forms 

HUNT.  ES.  BIO.  — 19 


rogs'  eggs  from  three  to  ten  hours  old.  All 
stages  from  four  cells  to  thirty-two  cells  may- 
be noted.  Photograph,  enlarged  four  times, 
by  Davison. 


290 


THE  VERTEBRATE  ANIMALS 


l:)ury  themselves  in  the  soft  mud  of  the  pond  bottom  during  the 

winter. 

Shortly  after  the  legs  appear,  the  gills  begin  to  be  absorbed,  and 

lungs  take  their  place.     At  this  time  the  young  animal  may  be 

seen  coming  to  the  surface  of  the 
water  for  air.  Changes  in  the 
diet  of  the  animal  also  occur; 
the  long,  coiled  intestine  is  trans- 
formed into  a  much  shorter  one. 
The  animal,  now  insectivorous 
in  its  diet,  becomes  provided 
with  tiny  teeth  and  a  mobile 
tongue,  instead  of  keeping  the 
horny  jaws  used  in  scraping  off 
algae.  After  the  tail  has  been 
completely  absorbed  and  the  legs 
have  become  full  grown,  there  is 
no  further  structural  change,  and 
the  metamorphosis  is  complete. 

The  Common  Toad.  —  One  of 
the  nearest  of  the  allies  of  the  frog 

is  the  common  toad.     The  eggs,  like  those  of  the  frog,  are  deposited 

in  fresh-water  ponds,  especially  small  pools.     The  egg-laying  season 

is  later  than  that  of  the  frog.     The  eggs  are  laid  in  strings,  as  many 

as  eleven  thousand  eggs 

having  been  laid  by  a 

single  toad. 

Suggestions  for  Field 
Work.  —  The  egg-laying 
season  in  New  York  state 
is  early  May.  At  this 
time  procure  a  female 
that  has  not  laid  her  eggs 
and  place  her  in  an  aqua- 
rium. If  undisturbed,  she 
may  lay  her  eggs  in  cap- 
tivity. Compare  the  bulk 
of  the  eggs  after  they  are 
laid  with  the  size  of  the 


in  tliL-  lifi'  ol  tadpulfsof  the  greeu 
frog.  The  two  large  tadpoles  are  in 
their  second  summer.  Photographed 
by  Overton. 


The 


comnion 


toad. 


THE   VERTEBRATE  ANIMALS 


291 


toad  that  laid  them.  This  apparent  discrepancy  is  caused  by  the  swelling 
of  the  gelatinous  substance  around  them.  If  possible,  count  the  number 
of  eggs  laid  by  one  female.^ 

Toad  tadpoles  may  be  distinguished  from  those  of  the  frog,  as 
they  are  darker  in  color,  and  have  a  more  slender  tail  and  a  rela- 
tively larger  body  than  those  of  the  frog.  The  metamorphosis 
occupies  only  about  two  months  in  the  vicinity  of  New  York, 
but  varies  greatly  with  the  temperature.  During  the  warm 
weather  the  tail  is  absorbed  with  wonderful  rapidity,  and  the 
change  from  a  tadpole  with  no  legs  to  that  of  the  small  toad 
living  on  land  is  often  accomplished  in  a  few  hours.  This  has 
given  rise  to  the  story  that  it  has  rained  toads,  because  during  the 
night  thousands  of  young  toads  have  changed  their  habitat  from 
the  water  to  the  land. 

The  toad  is  of  great  economic  importance  to  man  because  of  its 
diet.  No  less  than  eighty-three  species  of  insects,  mostly  injurious, 
have  been  proved  to  enter  into  the  dietary.^  A  toad  has  been  ob- 
served to  snap  up  one  hundred  and  twenty-eight  flies  in  half  an 
hour.  Thus  at  a  low  estimate  it  could  easily  destroy  one  hundred 
insects  during  a  day  and  do  an  immense  service  to  the  garden 
during  the  summer.  It  has  been  estimated  by  Kirkland  that  a 
single  toad  may,  on  account  of  the  cutworms  which  it  kills,  be  worth 
$19.88  each  season  it 
lives  if  the  damage 
done  by  each  cut- 
worm be  estimated  at 
only  one  cent.  Toads 
also  feed  upon  slugs 
and  other  garden 
pests. 


Other  Amphibians.  — 
The  tree  frogs  (called 
tree  toads)  are  familiar 


Spotted  salamander.     From    photograph  loaned  by 
the  American  Museum  of  Natural  History. 


to  us  in  the  early  spring  as  the  **  peepers  "  of  the  swamps.  They  are 
among  the  earliest  of  the  frogs  to  lay  their  eggs.  During  adult  life  they 
spend  most  of  their  time  on  the  trunks  of  trees,  where  they  receive  im- 

^  See  Hodge,  Nature  Study  and  Life. 

2  See  Kirkland,  Habits,  Food,  and  Economic  Importance  of  the  American  Toad. 
Bui.  46,  Hatch  Experiment  Station,  Amherst,  Mass. 


292  THE  VERTEBRATE  ANIMALS 

munity  from  attack  because  of  their  color  markings.  The  feet  of  the  tree 
toad  are  modified  for  climbing  by  having  little  disks  on  the  ends  of  the 
toes,  by  means  of  which  it  is  able  to  cling  to  vertical  surfaces. 

Another  common  amphibian  is  the  newt,  a  salamander.  This  smooth- 
skinned,  four-limbed  animal,  often  incorrectly  called  a  lizard,  passes  its 
larval  life  in  the  water,  where  it  breathes  by  means  of  external  gills.  Later 
it  loses  its  gills,  becomes  provided  with  lungs,  and  comes  out  on  land. 
Its  coat,  which  was  greenish  in  the  water,  now  becomes  bright  orange 
in  color.  In  this  condition  we  sometimes  find  them  crawling  on  wood 
roads  after  a  rain.  After  over  two  years'  life  on  land,  it  again  returns  to 
the  water,  becomes  green  with  red  spots  (as  seen  in  the  Figure),  and  now 
is  able  to  reproduce  its  kind.  Some  salamanders  never  have  lungs,  but 
breathe  through  the  moist  skin. 


Newt.     From  photograph  loaned  by  the  American  Museum  of  Natural  History, 

Still  other  amphibians  are  the  mud  puppies,  sirens  or  mud  eels,  and  the 
axolotl.  All  of  the  above  animals  differ  from  the  reptiles  in  having  a 
smooth  skin  with  no  scales,  and  in  passing  the  early  stage  of  their  existence 
in  the  water. 

Characteristics  of  Amphibia.  —  The  frog  belongs  to  the  class  of 

vertebrates  known  as  Amphibia.  As  the  name  indicates  (amphi, 
both,  and  hia,  life),  members  of  this  group  pass  more  or  less  of  their 
life  in  the  water,  although  in  the  adult  state  they  are  provided  with 
lungs.  In  the  earlier  stages  of  their  development  they  take  oxygen 
into  the  blood  by  means  of  gills.  At  all  times,  but  especially  during 
the  winter,  the  skin  serves  as  a  breathing  organ.  The  skin  is  soft 
and  unprotected  by  bony  plates  or  scales.  The  heart  has  three 
chambers,  two  auricles  and  one  ventricle.  Most  amphibians 
undergo  a  complete  metamorphosis. 

Classification  op  Amphibia  Mentioned 
Order  I.    Urodela.     Amphibia  having  usually  poorly  developed  appendages.     Tail 

persistent  through  life.     Examples  :  mud  puppy,  newt,  salamander. 
Order  II.    Anura.     Tailless  Amphibia,  which  undergo  a  metamorphosis,  breathing 

by  gills  in  larval  state,  by  lungs  in  adult  state.    Examples :  toad  and  frog. 


THE  VERTEBRATE  ANIMALS  293 

Reference  Books 

elementary 

Davison,  Practical  Zoology,  pages  199-211.     American  Book  Company. 
Herrick,  Textbook  in  General  Zoology,  Chap,  XX.     American  Book  Company. 
Hodge,  Nature  Study  and  Life,  Chaps.  XVI,  XVII.     Ginn  and  Company. 
Jordan,  Kellogg,  and  Heath,  Animal  Studies.     D.  Appleton  and  Company. 
Nature  Study  Leaflets,  Cornell  Nature  Study,  BuQetins  XVI,  XVII. 

ADVANCED 

Ditmars,    The  Batrachians  of  New  York.    Guide  Leaflet   19,   American    Museum 

of  National  Historj-. 
Dickinson,  The  Frog  Book.     Doubleday,  Page,  and  Company. 
Dickinson,  Salamanders.     Doubleday,  Page,  and  Company. 
Holmes,  The  Biology  of  the  Frog.     The  Macmillan  Company. 
Morgan,   The  Development  of  the  Frog's  Egg.     The  Macmillan  Company. 
Parker  and  Haswell,  Textbook  of  Zoology.     The  Macmillan  Company. 

Reptiles 

Turtles  and  Tortoises,  Adaptations  for  Life.  —  The  turtles  and 
tortoises,  the  latter  land  animals,  form  a  large  and  interesting 
group.  The  body  is  flattened,  and  is  covered  on  the  dorsal  and 
ventral  sides  by  a  bony  framework.  This 
covering  is  composed  of  plates  cemented  to 
the  true  bone  underneath,  the  whole  form- 
ing one  horny  cover.  This  covering,  an 
adaptation  for  protection,  is  more  perfect 
in  the  box  tortoise,  where  a  hinge  on  the 
ventral  side  allows  the  animal  to  retreat 
within  the  shell,  the  head  and  legs  being 

completely  covered.  Western  painted  turtle. 

Adaptations  for  Food  Getting.  —  The  long 
neck  and  powerful  horny  jaws  are  factors  in  the  food  procuring. 
Turtles  have  no  teeth.     Prey  is  seized  and  held  by  the  jaws,  the 
claws  of  the  front  legs  being  used  to  tear  the  food. 

Turtles  are  very  strong  for  their  size.  The  stout  legs  carry  the 
animal  slowly  on  land,  and  in  the  water,  being  slightly  webbed, 
they  are  of  service  in  swimming.  In  some  water  turtles  the  front 
limbs  are  modified  into  flippers  for  swimming.  The  strong  claws 
are  used  for  digging,  especially  at  egg-laying  season,  for  some 
turtles  dig  holes  in  sandy  beaches  in  which  the  eggs  are  deposited. 


294 


THE  VERTEBRATE  ANIMALS 


Box  tortoise  {Cistudo  Carolina).  From  photo- 
graph loaned  by  the  American  Museum  of 
Natural  History. 


Some  Different  Turtles.  — 
Turtles  are  mostly  aquatic  in 
habit.  Some  exceptions  are 
the  box  tortoise  {Cistudo  Caro- 
lina) and  the  giant  tortoise  of 
the  Galapagos  Islands.  Many 
of  the  sea-water  turtles  are  of 
large  size,  the  leatherback 
and  the  green  turtle  often 
weighing  six  hundred  to  seven 
hundred  pounds  each.  The 
flesh  of  the  green  turtle  and 
especially  the  diamond-back 
terrapin,  an  animal  found  in 
the  salt  marshes  along  our  southeastern  coast,  are  highly  esteemed  as  food. 
Unfortunately  for  the  preservation  of  the  species,  these  animals  are  usually 
taken  during  the  breeding  sea- 
son when  they  go  to  sandy 
beaches  to  lay  their  eggs. 

Lizards.  —  Lizards    may 

be  recognized  by  the  long 

body    with     four    legs    of 

nearly     equal    size.      The 

body  is  covered  with  scales. 

The  animal  never  lives  in 

water,  it  is  active  in  habit, 

and  it  does  not  undergo  a 

metamorphosis.  Lizards 

are  generally  harmless  creatures,  the  Gila  monster  of  New  Mexico 

and  Arizona,  a  poisonous  variety,  being  one  exception.    Lizards 

are  of  economic  importance  to  man,  because  they  eat  insects  and 

include  the  injurious 
ones  in  their  dietary. 
The  iguana  of  Central 
America  and  South 
America,  growing  to  a 
length  of  three  feet  or 
more,  has  the  distinc- 
tion of  being  one  of 
the  few  edible  lizards. 


The  Gila  monster.     Photograph  one  tenth  nat- 
ural size,  by  Davison. 


^mjm 


i3» 


A  garter  8nake,one  of  our  commonest  harmless  reptiles. 


THE  VERTEBRATE   ANIMALS 


295 


Snakes.  —  Probably  the  most  disliked  and  feared  of  all  animals 
are  the  snakes.  This  feeling,  however,  is  rarely  deserved,  for,  on 
the  whole,  our  common  snakes  are  beneficial  to  man.  The  black 
snake  and  the  milk  snake  feed  largely  on  injurious  rodents  (rats, 
mice,  etc.),  the  pretty  green  snake  eats  injurious  insects,  and  the 
little  DeKays  snake  feeds  partially  on  slugs.  If  it  were  not  that 
the  rattlesnake  and  the  copi  erhead  are  venomous,  they  also  could 
be  said  to  be  useful,  for  they  live  on  English  sparrows,  rats, 
mice,  moles,  and  rabbits. 

Snakes  are  almost  the  only  legless  vertebrates.  Although  the  limbs 
are  absent,  still  the  pelvic  and  pectoral  girdles  are  developed.  The  very 
long  backbone  is  made  up  of 
a  large  number  of  vertebrae, 
as  many  as  four  hundred 
being  found  in  the  boa  con- 
strictor. Ribs  are  attached 
to  all  vertebriB  in  the  region 
of  the  body  cavity. 

Locomotion. — Locomotion 
is  performed  by  pulling  and 
pushing  the  body  along  the 
ground,  a  leverage  being  ob- 
tained by  means  of  the  broad, 
flat  scales,  or  scutes,  with 
which  the  ventral  side  of  the 
body  is  covered.  Snakes 
may  move  without  twisting 
the  body.  This  is  accomplished  by  a  regular  drawing  forward  of  the 
scutes  and  then  pushing  them  backward  rather  violently. 

Feeding  Habits.  —  The  bones  of  the  jaw  are  very  loosely  joined  to- 
gether. Thus  the  mouth  of  the  snake  is  capable  of  wide  distention.  It 
holds  its  prey  by  means  of  incurved  teeth,  two  of  which  (in  the  poisonous 
snakes)  are  hoUow  or  grooved,  and  serve  as  a  duct  for  the  passage  of 
poison.  The  poison  glands  are  at  the  base  of  the  curved  fangs  in  the 
upper  jaw.  The  tongue  is  very  long  and  cleft  at  the  end.  It  is  an  organ 
of  touch  and  taste,  and  is  not,  as  many  people  believe,  used  as  a  sting. 
The  food  is  swallowed  whole,  and  pushed  down  by  ryhthmic  contractions 
of  the  muscles  surrounding  the  gullet.  They  usually  refuse  other  than 
living  prey. 

Adaptations.  —  Snakes  are  usually  protectively  colored.  They  are 
not  extremely  prolific  animals,  but  hold  their  own  with  other  forms  of 
life,  because  of  their  numerous  adaptations  for  protection,  their  noiseless 
movement,  protective  color,  and,  in  some  cases,  by  their  odor  and  poison. 


Skull  of  boa  constrictor,  two  thirds  natural  size. 
Note  the  inpointing  teeth.  Photograph  by 
Davison. 


296  THE  VERTEBRATE  ANIMALS 

Poisonous  Snakes.  —  Not  all  snakes  can  be  said  to  be  harmless.  The 
bite  of  the  rattlesnake  of  our  own  country,  although  dangerous,  seldom 
kills.  The  dreaded  cobra  of  India  has  a  record  of  over  two  hundred  and 
fifty  thousand  persons  killed  in  the  last  thirty-five  years.  The  Indian 
government  yearly  pays  out  large  sums  for  the  extermination  of  venomous 
snakes,  over  two  hundred  thousand  of  which  have  been  killed  during  a 
single  year. 

Alligators  and  Crocodiles.  —  The  latter  are  mostly  confined  to  Asia 
and  Africa,  while  the  former  are  natives  of  North  and  South  America. 
The  chief  structural  difference  between  them  is  that  the  teeth  in  alligators 


Young  alligator.     One  fourth  natural  size. 

are  set  in  long  sockets,  while  those  of  the  crocodile  are  not.  Both  of 
these  great  Uzardlike  animals  have  broad,  vertically  flattened  tails  adapted 
to  swimming.  The  eyes  and  tip  of  the  snout,  the  latter  holding  the  nos- 
tril holes,  protrude  from  the  head,  so  that  the  animal  may  float  motion- 
less near  the  surface  of  the  water  with  only  eyes  and  nostrils  visible.  The 
nostrils  are  closed  by  a  valve  when  the  animal  is  under  water.  These  rep- 
tiles feed  on  fishes,  but  often  attack  large  animals,  as  horses,  cows,  and 
even  man.  They  seek  their  prey  chiefly  at  night,  and  spend  the  day  bask- 
ing in  the  sun.  The  crocodiles  of  the  Ganges  River  in  India  levy  a  yearly 
tribute  of  many  hundred  lives  from  the  natives. 

Characteristics  of  Reptilia.  —  The  animals  described  belong 
to  the  class  of  vertebrates  known  as  Reptilia.  Such  animals 
are  characterized  by  having  scales  developed  from  the  skin.  These 
in  the  turtle  have  become  bony  and  are  connected  with  the  internal 
skeleton.  Reptiles  always  breathe  by  means  of  lungs,  differing  in 
this   respect   from   the   amphibians.     They   show   their   distant 


THE  VERTEBRATE  ANIMALS  297 

relationship  to  birds  in  that  their  large  eggs  are  incased  in  a  leath- 
ery, limy  shell. 

Classification  of  Reptilss 

Order  I.  Chelonia  (turtles  and  tortoises).  Flattened  reptiles  with  body  inclosed 
in  bony  case.  No  teeth  or  sternum  (breastbone).  Examples:  snapping 
turtle,  box  tortoise. 

Order  II.  Lacertilia  (lizards).  Body  covered  with  scales,  usually  having  two- 
paired  appendages.     Breathe  by  lungs.     Examples  :  fence  lizard,  horned  toad. 

Order  III.  Ophidia  (snakes).  Body  elongated,  covered  with  scales.  No  limbs 
present.     Examples :  garter  snake,  rattlesnake. 

Order  IV.  Crocodilia.  Fresh-water  reptiles  with  elongated  lx)dy  and  bony  scales 
on  skin.     Two  paired  limbs.     Examples  :  alligator,  crocodile. 

Reference  Books 

elementary 

Davison,  Practical  Zoology,  pages  211-226.     American  Book  Company. 

Ditmars,  The  Reptiles  of  New  York.    Guide  Leaflet  20,  American  Museum  of  Natural 

History. 
Herrick,  Textbook  in  General  Zodlogy,  Chap.  XXI.     American  Book  Company. 
Jordan,   Kellogg,   and  Heath,  Animal  Studies,  Chap.   XVI.      D.   Appleton    and 

Company. 

advanced 

Ditmars,  The  Reptile  Book.     Doubleday,  Page,  and  Company. 
Parker  and  Haswell,  Textbook  of  Zodlogy.     The  Macmillan  Company. 
Riverside  Natural  History.     Houghton,  MifSin,  and  Company. 

Birds 

Problem  XXXIX,  Study  of  some  adaptations  in  and  re- 
actions of  birds.    {Laboratory  Manual,  Prob.  XXXIX.) 

Adaptations.  —  Birds  among  all  other  animals  are  known  by 
their  covering  of  feathers  and  the  peculiar  modification  of  the  fore 
limbs  for  flight.  In  no  other  group  of  animals  may  we  study 
adaptations  so  well  as  here. 

Field  Work.  —  Bird  activities  may  best  be  studied  out  of  doors.  Any 
city  park  offers  more  or  less  opportunity  for  such  study,  for  several  of 
our  native  birds  make  the  parks  their  home.  If  not  these,  then  the  Eng- 
Ush  sparrow  can  be  found  anywhere  in  the  East.  The  best  time  for 
making  observations  is  early  in  the  morning,  especially  in  the  spring 
season. 

Body.  —  The  body  of  a  bird,  under  its  covering  of  feathers,  is 
rounded  and  more  or  less  pointed  at  each  end.     Powerful  muscles, 


298 


THE  VERTEBRATE  ANIMALS 


attached  to  the  wings,  aid  in  locomotion,  while  the  wing  itself,  a 
modified  arm,  is  one  of  the  most  evident  adaptations  to  life  in  the 
air. 

Flight.  —  Watch  a  bird  in  flight.  The  tip  of  the  wing  usually 
describes  a  curve  which  results  in  the  forming  of  the  figure  8. 
The  rate  of  movement  of  the  wing  differs  greatly  in  different  birds. 

The  wing  of  a  bird  is  slightly  concave 
on  the  lower  surface  when  outstretched. 
Thus  on  the  downward  stroke  of  the 
wing  more  resistance  is  offered  to  the 
air.  Birds  with  long,  thin  wings,  as 
the  hawks  and  gulls,  move  the  wing 
in  flight  with  much  less  rapidity  than 
those  with  short,  wide  wings,  as  the 
grouse  or  quail.  The  latter  birds  start 
with  much  less  apparent  effort  than 
the  birds  with  longer  wings ;  they  are, 
however,  less  capable  of  sustained 
flight. 

Feathers.  ^-  Few  people  realize  that 
the  body  of  a  bird  is  not  completely 
covered  with  feathers.  Featherless 
areas  can  be  found  on  the  body  of 
any  common  bird,  although  tiny  "  pin 
feathers  "  are  found  on  such  areas  as 
well  as  on  other  parts  of  the  body. 
Soft  down  feathers  cover  the  body, 
serving  for  bodily  warmth.  Larger 
feathers  give  the  rounded  contour  to 
the  body.  In  the  wings  we  find  quill 
feathers ;  these  are  adapted  for  service 
in  flight  by  having  a  long  hollow  shaft, 
from  which  lateral  interlocking 
branches  are  given  off,  the  whole 
making  a  light  structure  offering  considerable  resistance  to  the 
air.  Feathers  are  developed  from  the  outer  layer  of  the  skin,  and 
are  formed  in  almost  exactly  the  same  manner  as  are  the  scales 
of  a  fish  or  a  lizard.     The  first  feathers  developed  on  the  body 


1 

^^HpT^H 

^^■^1 

1 

^^^^K^  wb^^^I 

^^^H&N  P'VjflB^B 

I^H  -^umi 

t!^    ■^m^BHH 

K'  1  ^ 

^Bkl  mB^M 

Feathers  of  a  meadow  lark. 
Which  of  the  above  are  used 
for  flight  ?  How  do  you  know  ? 
From  photograph  loaned  by 
the  American  Museum  of  Nat- 
ural History. 


THE  VERTEBRATE  ANIMALS  299 

are  evidently  for  protection  against  cold  and  wet,  but  later  in  life 
they  serve  other  uses.  The  feathers  of  most  male  birds  are 
brightly  colored.  This  seems  to  make  them  attractive  to  the 
females  of  the  species ;  thus  the  male  may  win  its  mate. 

Adaptations  in  the  Lower  Limbs. — The  ankle  of  a  bird  is  extremely 
long  and  reptile-like.  Scales  are  found  on  the  ankle  and  foot.  The 
most  extraordinary  adaptations  are  found  in  the  feet  of  various 
birds.    Some  have  the  foot  adapted  to  perching,  others  for  swim- 


Adaptations  in  the  feot  of  birds.  Explain,  after  reading  the  paragraph  on  adapta- 
tion in  the  lower  limbs,  how  each  of  the  above  feet  is  fitted  to  do  its  work. 
From  photograph  loaned  by  the  American  Museum  of  Natural  History. 

ming,  others  wading,  etc.  We  are  able,  by  looking  at  the  feet  of  a 
bird,  to  decide  almost  certainly  its  habitat,  method  of  hfe,  and  per- 
haps its  food. 

In  the  perching  birds  we  find  three  toes  in  front  and  one  behind, 
the  hind  toe  playing  an  important  part  in  holding  the  foot  in  place. 
In  swallows,  rapid  and  untiring  flyers,  the  feet  are  small.  In  the 
case  of  the  parrots,  where  the  foot  is  used  for  holding  food,  climbing, 
and  clinging,  we  find  the  four-clawed  toes  arranged  two  in  front  and 


300 


THE  VERTEBRATE  ANIMALS 


two  behind.     Hawks  and  eagles  are  provided  with  strong  talons 
with  which  the  prey  is  seized  and  killed. 

Adaptation  for  semiaquatic  life  is  seen  in  plovers,  herons,  or 
storks,  where  long  legs  and  long  toes  enable  the  birds  to  seek  their 
food  in  soft  mud  among  reeds  or  lily  pads,  or  along  sand  fiats. 
True  aquatic  birds,  on  the  other  hand,  are  provided  with  webbed 
toes.  The  foot  of  the  common  barnyard  duck,  for  example,  is 
much  like  that  of  the  alligator.  In  the  ostrich  and  cassowary 
the  wings  are  not  used  for  flight ;  here  the  lower  limbs  have  taken 
up  the  function  of  rapid  motion. 

Perching.  —  The  habit  of  perching  is  an  interesting  one.  In 
many  perching  birds  the  tendons  of  the  leg  and  foot,  which  regulate 

the  toes,  are  self -locking ;  while 
asleep  such  birds  hold  themselves 
perfectly.  A  certain  part  of  the 
ear,  known  as  the  semicircular  ca- 
nals, has  to  do  with  the  function  of 
balancing.  In  the  flamingoes  and 
other  birds,  which  do  not  perch, 
balancing  appears  to  be  automatic ; 
thus  the  bird  is  able  to  sleep  when 
in  an  upright  position. 

Tail.  —  The  tail  is  sometimes 
used  in  balancing;  its  chief  func- 
tion, however,  appears  to  be  that 
of  a  rudder  during  flight.  Most 
birds  have  under  the  skin  of  the 
tail  a  large  oil  gland,  whence  comes 
the  supply  of  oil  that  is  used  in 
waterproofing  the  feathers  in  preen- 
ing. 

The  Skeleton.  —  The  skeleton 
combines  lightness,  flexibility,  and 
strength.  Many  bones  are  hollow 
or  have  large  spongy  cavities. 
The  bones  of  the  head  and  neck  show  many  and  varied  adaptations 
to  the  life  that  the  bird  leads.  The  vertebrae  which  form  the  frame- 
work of  the  neck  are  strong  and  flexible.    They  vary  in  shape  and 


Skeleton  of  a  fowl :  C,  clavicle  ;  CV, 
cervical  vertebrae ;  K,  keeled  ster- 
num ;  PG,  pelvic  girdle  ;  PcG,  bones 
of  pectoral  girdle  (except  clavicle). 


THE  VERTEBRATE  ANIMALS 


301 


in  number.  The  swan,  seeking  its  food  under  water,  has  a  neck 
containing  twenty-three  long  vertebrae ;  the  EngHsh  sparrow,  in  a 
different  environment,  has  only  fourteen  short  ones.  Some  bones, 
notably  the  breastbone,  are  greatly  developed  in  flying  birds  for 
the  attachment  of  the  muscles  used  in  flight. 

Bill.  —  The  form  of  the  bill  shows  adaptation  to  a  wonderful 
degree,  the  bills  varying  greatly  according  to  the  habits  of  the  birds. 


Adaptations  in  the  bills  of  birds.  Could  we  tell  anything  about  the  food  of  a 
bird  from  its  bill?  Do  these  birds  all  get  their  food  in  the  same  manner? 
Do  they  all  eat  the  same  kind  of  food  ? 


A  duck  l.«as  a  flat  bill  for  pushing  through  the  mud  and  straining 
out  the  food ;  a  bird  of  prey  has  a  curved  or  hooked  beak  for 
tearing;  the  woodpecker  has  a  sharp,  straight  bill  for  piercing 
the  bark  of  trees  in  search  of  the  insect  larvae  which  are  hidden 
underneath. 

Birds  do  not  have  teeth.  The  edge  of  the  bill  may  be  toothlike, 
as  in  some  fish-eating  ducks;  these,  however,  are  not  true  teeth. 
Frequently  the  tongue  has  sharp  toothUke  edges  which  serve 
the  same  purpose  as  the  recurved  teeth  of  the  frog  or  snake. 

Adaptations  for  Active  Life.  —  The  rate  of  respiration,  of  heart- 
beat, and  the  body  temperature  are  all  higher  in  the  bird  than  in 
man.  ^ 


302  THE  VERTEBRATE  ANIMALS 

This  is  one  of  the  greatest  adaptations  to  the  active  life  led  by  a 
bird.  Man  breathes  from  twelve  to  fourteen  times  per  minute. 
Birds  breathe  from  twenty  to  sixty  times  a  minute.  The  lungs  are 
not  large,  the  bronchial  tubes  being  continued  through  the  lungs 
into  hollow  spaces  filled  with  air,  which  are  found  between  the 
organs  of  the  body.  Only  the  lungs,  however,  are  used  for  breath- 
ing. Because  of  the  increased  activity  of  a  bird,  there  comes  a 
necessity  for  a  greater  and  more  rapid  supply  of  oxygen,  an  increased 
blood  supply  to  carry  the  material  to  be  used  up  in  the  release  of 
energy,  and  a  means  of  rapid  excretion  of  the  wastes  resulting  from 
the  process  of  oxidation.  A  bird  may  be  compared  to  a  high-pres- 
sure steam  engine ;  in  order  to  release  the  energy  which  it  uses  in 
flight,  a  large  quantity  of  fuel  which  will  oxidize  quickly  must  be 
used.  Birds  are  large  eaters,  and  the  digestive  tract  is  fitted  to 
digest  the  food  quickly  and  to  release  the  energy  when  needed,  by 
having  a  large  crop  in  which  food  may  be  stored  in  a  much  softened 
condition.  As  soon  as  the  food  is  part  of  the  blood,  it  may  be  sent 
rapidly  to  the  places  where  it  is  needed,  by  means  of  the  large  four- 
chambered  heart  and  large  blood  vessels. 

The  high  temperature  of  the  bird  is  a  direct  result  of  this  rapid 
oxidation;  furthermore,  the  feathers  and  the  oily  skin  form  an 
insulation  which  does  not  readily  permit  of  the  escape  of  heat. 
This  insulating  cover  is  of  much  use  to  the  bird  in  its  flights  at 
high  altitudes,  where  the  temperature  is  often  very  low. 

The  Nervous  System  and  the  Senses. — The  central  nervous  system 
is  well  developed.  A  large  forebrain  is  found,  which,  according  to  a  series 
of  elaborate  experiments  with  pigeons,  is  found  to  have  to  do  with  the 
conscious  life  of  the  bird.  The  cerebellum  takes  care  of  the  acts  which  are 
purely  mechanical. 

Sight  is  probably  the  best  developed  of  the  senses  of  a  bird.  The  keen- 
ness of  vision  of  a  hawk  is  proverbial.  It  has  been  noticed  that  in  a  bird 
which  hunts  its  prey  at  night,  the  eyes  look  toward  the  front  of  the  face. 
In  a  bird  which  is  hunted,  as  in  the  dove,  the  eyes  are  placed  at  the  side 
of  the  head.  In  the  case  of  the  woodcock,  which  feeds  at  night  in  the 
marshes,  and  which  is  in  constant  danger  from  attack  by  owls,  the  eyes 
have  come  to  lie  far  back  on  the  top  of  the  head.  Hearing  is  also  well 
developed  in  most  birds;  this  fact  may  be  demonstrated  with  any 
canary. 

The  sense  of  smell  does  not  appear  to  be  well  developed  in  any  bird,  and 
is  especially  deficient  in  seed-eating  birds. 


THE  VERTEBRATE  ANIMALS 


303 


Nesting  Habits.  —  Among  the  most  interesting  of  all  instincts 
shown  by  birds  are  the  liabits  of  nest  building.  We  have  found 
that  some  invertebrates,  as  spiders  and  ants,  protect  the  eggs  when 
laid.  In  the  vertebrate 
group  some  fishes  (as  the 
sunfish  and  stickleback) 
make  nests  for  the  depo- 
sition of  the  eggs.  But 
most  fishes,  and  indeed 
other  vertebrates  lower 
than  the  birds,  leave  the 
eggs  to  be  hatched  by  the 
heat  of  the  sun.  Birds  in- 
cubate their  eggs,  that  is, 
hatch  them,  by  the  heat  of  .      ,    ,       « 

, ,     .  IT  TT  Nest  of  a  phcebe  under  the  barn  floor. 

thei^:  own  bodies,     llence 

a  nest,  in  which  to  rest,  is  needed.  The  ostrich  is  an  exception; 
it  makes  no  nest,  but  the  male  and  the  female  take  turns 
in  sitting  on  the  eggs.  Such  birds  as  are  immune  from  the 
attack  of  enemies  because  of  their  isolation  or  their  protective 

coloration  (as  the  puffins, 
gulls,  and  terns),  build  a 
rough  nest  among  the  rocks 
or  on  the  beach.  The  eggs, 
especially  those  of  the  tern, 
are  marked  and  colored  so 
as  to  be  almost  indistin- 
guishable from  the  rocks  or 
sand  on  which  they  rest. 
Other  birds  have  made  the 
nest  a  home  and  a  place  of 
refuge  as  well  as  a  place  to 
hatch  the  eggs.  Such  is  the 
nest  of  the  woodpecker  in 
the  hollow  tree  and  the  hang- 
ing nest  of  the  oriole.  Some  nests  which  might  be  easily  seen  be- 
cause of  their  location  are  often  rendered  inconspicuous  by  the 
builders ;  for  example,  the  lichen-covered  nest  of  the  humming  birds. 


Nest  of  the  chimney  swift. 


304  THE  VERTEBRATE  ANIMALS 

Care  of  the  Young. — After  the  eggs  have  been  hatched,  the  young 
in  most  cases  are  quite  dependent  upon  the  parents  for  food.  Most 
young  birds  are  prodigious  eaters;  as  a  result  they  grow  very 
rapidly.     It  has  been  estimated  that  a  young  robin  eats  two  or 


Common  tern   {Sterna  hirundo)  and  young,  showing  nesting   and   feeding  habits. 
From  group  at  American  Museum  of  Natural  History. 

three  times  its  own  weight  in  worms  every  day.  Many  other  young 
birds,  especially  kingbirds,  are  rapacious  insect  eaters.  In  the  case 
of  the  pigeons  and  some  other  birds,  food  is  swallowed  by  the  mother, 
partially  digested  in  the  crop,  and  then  regurgitated  into  the  mouths 
of  the  young  nestlings. 

Problem  XL,  How  birds  are  of  economic  importance.  (Lab- 
or atorj/  Manual,  Prob.  XL.) 

Food  of  Birds.  —  The  food  of  birds  makes  them  of  the  greatest 
economic  importance  to  our  country.  This  is  because  of  the  rela- 
tion of  insects  to  agriculture.  A  large  part  of  the  diet  of  most  of 
our  native  birds  includes  insects  harmful  to  vegetation.     Investi- 


THE  VERTEBRATE  ANIMALS 


305 


gallons  undertaken  by  the  United  States  Department  of  Agricul- 
ture (Division  of  Biological  Survey)  show  that  a  surprisingly  large 
number  of  birds  once  believed  to 
harm  crops  really  perform  a  serv- 
ice by  killing  injurious  insects. 
Even  the  nmch  maligned  crow 
lives  to  some  extent  upon  insects. 
During  the  entire  year,  the  crow 
has  been  shown  to  eat  about  25 
per  cent  insect  food  and  29  per 
cent  grain.  In  May,  when  the 
grain  is  sprouting,  the  crow  is  a 
pest,  but  he  makes  up  for  it  dur- 
ing the  remainder  of  the  summer 
by  eating  harmful  insects.  The 
robin,  whose  presence  in  the 
cherry  tree  we  resent,  during  the 
rest  of  the  summer  does  untold 
good  by  feeding  upon  noxious  in- 
sects. Birds  use  the  food  sub- 
stances which  are  most  abundant 
around  them  at  the  time.^ 

Not  only  do  birds  aid  man  in  his  battles  with  destructive  insects, 
but  seed-eating  birds  eat  the  seeds  of  weeds.  Our  native  sparrows 
(not  the  English  sparrow),  the  doves,  partridges,  and  other  forms 
feed  largely  upon  the  seeds  of  many  of  our  common  weeds.  This 
fact  alone  is  sufficient  to  make  birds  of  vast  economic  importance. 

*  The  following  quotation  from  I.  P.  Trimble,  A  Treatise  on  the  Insect  Enemies 
of  Fruit  and  Shade  Trees,  bears  out  this  statement :  "  On  the  fifth  of  May,  1864,  .  .  . 
seven  different  birds  .  .  .  had  been  feeding  freely  upon  small  beetles.  .  .  .  There 
was  a  great  flight  of  beetles  that  day ;  the  atmosphere  was  teeming  with  them. 
A  few  days  after,  the  air  was  filled  with  Ephemera  flies,  and  the  same  species  of  birda 
were  then  feeding  upon  them." 

During  the  outbreak  of  Rocky  Mountain  locusts  in  Nebraska  in  1874-1877, 
Professor  Samuel  Aughey  saw  a  long-billed  marsh  wren  carry  thirty  locusts  to  her 
young  in  an  hour.  At  this  rate,  for  seven  hours  a  day,  a  brood  would  consume  210 
locusts  per  day,  and  the  passerine  birds  of  the  eastern  half  of  Nebraska,  allowing 
only  twenty  broods  to  the  square  mile,  would  destroy  daily  162,771,000  of  the 
pests.  The  average  locust  weighs  about  fifteen  grains,  and  is  capable  each  day  of 
con.suming  its  own  weight  of  standing  forage  crops,  which  at  $10  per  ton  would  be 
worth  S1743.26.  This  case  may  serve  as  an  illustration  of  the  vast  good  that  is 
HUNT.  ES.  BIO. 20 


Food  of  some  common  birds. 


306  THE  VERTEBRATE  ANIMALS 

Not  all  birds  are  seed  or  insect  feeders.  Some,  as  the  cormorants, 
ospreys,  gulls,  and  terns,  are  active  fishers.  Near  large  cities 
gulls  especially  act  as  scavengers,  destroying  much  floating  gar- 
bage that  otherwise  might  be  washed  ashore  to  become  a  menace  to 
health.  Sea  birds  also  live  upon  shellfish  and  crustaceans  (as 
small  crabs,  shrimps,  etc.) ;  some  even  eat  lower  organisms. 
The  kea  parrot,  once  a  fruit  eater,  now  takes  its  meal  from  the 
muscles  forming  the  backs  of  living  sheep.  Birds  of  prey  (owls) 
eat  living  mammals,  including  many  rodents,  for  example,  field 
mice,  rats,  and  other  pests. 

Extermination  of  our  Native  Birds.  —  Within  our  own  times  we 
have  witnessed  the  almost  total  extermination  of  some  species  of 
our  native  birds.  The  American  passenger  pigeon,  once  very 
abundant  in  the  Middle  West,  is  now  practically  extinct.  Audu- 
bon, the  greatest  of  all  American  bird  lovers,  gives  a  graphic 
account  of  the  migration  of  a  flock  of  these  birds.  So  numerous 
were  they  that  when  the  flock  rose  in  the  air  the  sun  was  dark- 
ened, and  at  night  the  weight  of  the  roosting  birds  broke  down  large 
branches  of  the  trees  in  which  they  rested.  To-day  hardly  a 
single  specimen  of  this  pigeon  can  be  found,  because  they  were 
slaughtered  by  the  hundreds  of  thousands  during  the  breeding 
season.  At  the  present  time  nearly  $3000  is  offered  to  the  person 
finding  a  pair  of  nesting  passenger  pigeons.  The  wholesale  killing 
of  the  snowy  egret  to  furnish  ornaments  for  ladies'  headwear 
is  another  example  of  the  improvidence  of  our  fellow-countrymen. 
Charles  Dudley  Warner  said,  ''  Feathers  do  not  improve  the  ap- 
pearance of  an  ugly  woman,  and  a  pretty  woman  needs  no  such 
aid."  Wholesale  kiUing  for  plumage,  eggs,  and  food,  and,  alas, 
often  for  mere  sport,  has  caused  the  decrease  of  our  birds  to  46 
per  cent  in  thirty  states  and  territories  within  the  past  fifteen  years. 
Every  crusade  against  indiscriminate  killing  of  our  native  birds 

done  every  year  by  the  destruction  of  insect  pests  fed  to  nestling  birds.  And  it 
should  be  remembered  that  the  nesting  season  is  also  that  when  the  destruction  of 
injurious  insects  is  most  needed ;  that  is,  at  the  period  of  greatest  agriciJtural 
activity  and  before  the  parasitic  insects  can  be  depended  on  to  reduce  the  pests. 
The  encouragement  of  birds  to  nest  on  the  farm  and  the  discouragement  of  nest 
robbing  are  therefore  more  than  mere  matters  of  sentiment ;  they  return  an  actual 
cash  equivalent,  and  have  a  definite  bearing  on  the  success  or  failure  of  the  crops. — • 
Year  Book  of  the  Department  of  Agriculture. 


THE  VERTEBRATE  ANIMALS 


307 


should  be  welcomed  by  all  thinking  Americans.  Without  the 
birds  the  farmer  would  have  a  hopeless  fight  against  insect  pests. 
The  effect  of  killing  native  birds  is  now  well  seen  in  Italy 
and  Japan,  where  insects  are  increasing  and  do  greater  damage 
each   year  to  crops  and  trees. 

Of  the  eight  hundred  or  more  species  of  birds  in  the  United 
States,  only  two  species  of  hawks  (Cooper's  and  the  sharp-shinned 
hawk),  the  great  horned  owl,  the  cowbird,  and  the  EngHsh  spar- 
row may  be  considered  as  enemies  of  man. 

The  English  Sparrow.  —  The  English  sparrow  is  an  example  of 
a  bird  introduced  for  the  purpose  of  insect  destruction,  that  has 
done  great  harm  because  of  its  relation 
to  our  native  birds.  Introduced  at 
Brooklyn  in  1850  for  the  purpose  of  ex- 
terminating the  cankerworm,  it  soon 
abandoned  an  insect  diet  and  has  driven 
out  most  of  our  native  insect  feeders. 
Investigations  by  the  United  States 
Department  of  Agriculture  have  shown 
that  in  the  country  these  birds  and 
their  young  feed  to  a  large  extent  upon 
grain,  thus  showing  them  to  be  injurious  The  proportions  of  food  of  the 
to  agriculture.     Dirty  and  very  prolific,  ^^  la   sp  r 

it  already  has  worked  its  way  from  the  East  as  far  as  the  Pacific 
coast.  In  this  area  the  bluebird,  song  sparrow,  and  yellowbird 
have  all  been  forced  to  give  way,  as  well  as  many  larger  birds  of 
great  economic  value  and  beauty.  The  English  sparrow  has  be- 
come a  national  pest,  and  should  be  exterminated  in  order  to  save 
our  native  birds.  It  is  feared  in  some  quarters  that  the  English 
starling  which  has  recently  been  introduced  into  this  country  may 
in  time  prove  a  pest  as  formidable  as  the  English  sparrow. 

Geographical  Distribution  and  Migrations.  —  Most  of  us  are 
aware  that  some  birds  remain  with  us  in  a  given  region  during  the 
whole  year,  while  other  birds  appear  with  the  approach  of  spring, 
departing  southwards  with  the  warm  weather  in  the  fall  of  the 
year.  Such  birds  we  call  migrants,  while  those  that  remain  the 
year  round  are  called  residents. 

In  Europe,  where   the  problem  of    bird  migration  has  been 


308        THE  VERTEBRATE  ANIMALS 

studied  carefully,  migrations  appear  to  take  place  along  well- 
defined  paths.  These  paths  usually  follow  the  coast  very  exactly, 
although  in  places  they  may  take  the  line  of  coast  that  existed  in 
former  geological  times.  In  this  country  the  Mississippi  valley,  a 
former  arm  of  the  sea,  forms  one  line  of  migration,  while  the  north 
Atlantic  seacoast  forms  another  route/ 

It  has  been  shown  that  the  southern  movement  of  migratory 
birds  in  the  fall  of  the  year  is  not  due  entirely  to  the  advent  of  cold 
weather,  but  is  largely  a  matter  of  adjustment  to  food  supply. 
A  migrant  almost  always  depends  upon  fruits,  seeds,  and  grains  as 

part  of  its  food.  Most  win- 
ter residents,  as  the  crow,  are 
omnivorous  in  diet.  Others, 
as  the  sparrows,  may  be  seed 
eaters,  but  under  stress  may 
change  their  diet  to  almost 
anything  in  the  line  of  food ; 
still  others,  as  the  wood- 
peckers, although  insect-eat- 
ing birds,  manage  to  find  the 
desired  food  tucked  away 
under  the  bark  of  trees. 
Many  insect-eating  birds, 
however,  because  their  food 
is  found  on  green  plants, 
appear  to  be  forced  south- 
ward by  the  cold  weather. 

Classification  of  Birds. — ■ 

African  ostrich  {Struthio  camelus).  ^^^^'  are  divided  into  two  great 

groups,  depending  on  the  de- 
velopment of  the  keel;  that  is,  the  part  of  the  breastbone  to  which  the 
muscles  used  in  flight  are  attached.  Hence  all  flying  birds  are  placed  in 
a  group  called  the  Carinatoe. 

Birds  in  which  the  keel  of  the  breastbone  is  not  well  developed,  such 

1  There  is  opportunity  for  a  careful  observer  to  learn  much  of  the  spring  or  fall 
migrations  in  the  particular  part  of  the  country  in  which  he  resides.  All  informa- 
tion thus  obtained  should  be  sent  to  the  secretary  of  the  American  Ornithologists' 
Union  or  to  W.  W.  Cooke  of  the  Biological  Survey,  who  has  done  much  to  estab- 
lish what  we  already  know  about  bird  migration  in  this  country. 


THE   VERTEBRATE  ANIMALS 


309 


White-throated  spairow  {Zonotrichia  albicoUia). 


as  the  ostrich  and  cassowary, 
are  said  to  belong  to  the 
liatilw.  These  birds  make 
up  for  their  lack  of  wing  de- 
velopment by  having  the  legs 
strong  and  long. 

The  flying  birds  are 
further  subdivided  into  a 
number  of  orders,  the  clas- 
sification based  upon  the 
adaptations  of  dififerent  parts 
of  the  bird,  especially  the  legs 
and  feet,  the  wings  and  the 

bill,  to  different  functions.  We  shall  not  trouble  ourselves  to  learn  all 
the  different  groups,  but  shall  content  ourselves  with  picking  out  some  of 
the  more  evident  and  important  ones,  especially  those  which  we  might 

meet  in  field  trips. 

I.  Perching  Birds.  —  To 
this  order  belong  most  of  our 
common  birds,  —  sparrows, 
swallows,  larks,  blackbirds, 
orioles,  kingbirds,  and  many 
others  well  known  to  every 
bird  lover.     In  this  group  the 


toes  are  so  placed,  three  toes 
being  turned  forward  and  one 
backward,  as  to  be  perfectly 
adapted  to  perching.  A  large 
number  of  our  sweetest  song- 
sters belong  among  the  perch- 
ers,  the  warblers,  wrens, 
thrushes,  bluebirds,  and,  last 
but  not  least,  our  robin. 

II.  The  Fowls  or  Gallina- 
ceous Birds.  —  This  order  is 
of  great  economic  impor- 
tance. From  the  jungle  fowl, 
found  wild  in  the  jungles  of 
India,  most  of  our  domesti- 
cated fowls  have  descended. 


A,  ptarmigan  in  winter;  B,  ptarmigan  in 
summer.  How  do  you  account  for 
the  change  in  plumage  ?  May  this 
change  be  of  use  to  the  bird  ? 


310 


THE   VERTEBRATE  ANIMATE 


Other  familiar  examples  are  the  turkeys,  quails,  partridge  or  ruffed  grouse, 
and  the  pheasants  and  prairie  chickens.  In  this  group  the  legs  are  strong 
and  stout,  the  body  thickset,  the  bill  and  claws  rather  blunt.  Birds  of 
this  order  do  not  fly  far  in  a  state  of  nature,  preferring  to  live  on  or 
near  the  ground.  Such  birds  as  the  ruffed  grouse,  which  nest  on  the 
ground,  are  almost  invariably  protectively  colored.  Another  interesting 
example  of  protective  resemblance  in  this  group  is  seen  in  the  ptarmigan. 
This  bird  in  the  winter  is  white  as  the  snow  which  surrounds  it ;    in  the 

spring  it  molts,  turning  to  a  gray 
and  white,  thus  resembling  the 
lichens  among  which  it  feeds. 

III.  Birds  of  Prey.  —  These 
birds  are  characterized  by  the 
strong  hooked  beak,  adapted  to 
tearing,  and  by  the  sharp  claws, 
which  are  curved  and  strong. 
Members  of  this  group  that  are 
best  known  to  us  are  the  hawks, 
the  condor,  with  its  great  sweep 
of  ten  feet  from  wing  to  wing, 
and  the  eagle. 

IV.  Waders.  —  These  are  birds 
with  unusually  long  legs  and  long 
necks,  the  latter  character  being 
a  natural  correlation  of  greatest 
service  in  food  getting.  Examples 
are  the  mud  hen  or  coot,  the  snipe, 
crane,  heron,  and  stork.  The  last 
two  are  the  giants  of  the  group. 

The  Swimmers  and  Divers.  —  Birds  placed  in  these  orders  have  the 
feet  webbed  ;  the  wings  are  often  adapted  for  long  and  swift  flight.  In 
this  division  are  placed  the  gulls,  terns,  ducks,  geese,  loons,  auks,  and 
puffins. 

Other  Orders.  —  Other  orders  of  birds  include  the  doves,  the  only 
remaining  native  representative  being  the  mourning  dove;  the  wood- 
peckers, strong  and  long  of  bill,  the  friend  of  the  lumberman  as  a  savior 
of  the  trees  from  boring  pests  which  live  under  the  bark ;  the  swifts  and 
humming  birds,  the  latter  among  the  tiniest  of  all  vertebrate  animals  ;  and 
the  parrots,  of  which  we  have  only  one  native  form,  the  Carolina  paroquet 
(Conurus  carolinensis) .  This  bird  once  had  a  range  north  as  far  as  the 
Great  Lakes ;    now  it  is  found  only  in  South  America. 

Relationship  of  Birds  and  Reptiles.  —  The  birds  afford  an  interesting 
example  of  how  the  history  of  past  ages  of  the  earth  has  given  a  clew  to 
the  structural  relation  which  birds  bear  to  other  animals.  Several  years 
ago,  two  fossil  skeletons  were  found  in  Europe  of  a  birdlike  creature  which 


Golden  eagle  (Aquila  chrysaUos).  North 
America  and  Europe.  Copyright,  1901, 
by  N.Y.  Zoological  Society. 


THE   VERTEBRATE  ANIMALS  311 

had  not  only  wings  and  feathers,  but  also  teeth  and  a  lizardlike  tail. 
From  these  fossil  remains  and  certain  structures  (as  scales)  and  habits 
(as  the  egg-laying  habits),  naturalists  have  concluded  that  birds  and  rep- 
tiles in  distant  times  were  nearly  related  and  that  our  existing  birds 
probably  developed  from  a  reptile-like  ancestor  millions  of  years  ago. 

Classification  of  Birds 

Division  I.   Ratitoe.     Running    birds    with    no    keeled    breastbone.     Examples* 

ostrich,  cassowary. . 
Division  II.    Carinatce.     Birds  with  keeled  breastbone. 

Order  i.  Passeres.  Perching  birds ;  three  toes  in  front,  one  Ijehind.  One  half 
of  all  species  of  birds  are  included  in  this  order.  Examples  :  sparrow,  thrush, 
swallow. 

Order  ii.  Gallince.  Strong  legs;  feet  adapted  to  perching.  Beak  stout.  Ex- 
amples :    jungle  fowl,  grouse,  quail,  domestic  fowl. 

Order  III.  Raptores.  Birds  of  prey.  Hooked  beak.  Strong  claws.  Examples: 
eagle,  hawk,  owl. 

Order  iv.  Grallatores.  Waders.  Long  neck,  beak,  and  legs.  Examples  :  snipe, 
crane,  heron. 

Order  v.  Natatores.  Divers  and  swimmers.  Legs  short,  toes  webbed.  Ex- 
amples :   gull,  duck,  albatross. 

Order  vi.  Columhce.  Like  Gallinae,  but  with  weaker  legs.  Examples ;  dove, 
pigeon. 

Order  vii.  PicaruB.  Woodpeckers.  Two  toes  point  forward,  two  backward, 
and  adaptation  for  climbing.     Long,  strong  bill. 

Reference  Books 
elementary 

Walker,  Our  Birds  and  their  Nestlings,     American  Book  Company. 
Beebe,  The  Bird.     Henry  Holt  and  Company. 

Nature  Study  Leaflets,  XXII,  XXIII,  XXIV,  XXV,  Cornell   Nature  Study  Bulle- 
tins. 
Walter,  H.  E.  and  H.  A.,  Wild  Birds  in  City  Parks. 

advanced 

Apgar,  Birds  of  the  United  States.     American  Book  Company. 

Bulletins  of  U.S.  Department  of  Agriculture,  Division  of  Biological  Survey,  Nos.  1, 

6,  15,  17.     See  also  Yearbook,  1899,  etc. 
Chapman,  Bird  Life.     D.  Appleton  and  Company. 
Riverside  Natural  History,  Vol.  IV.     Houghton,  Mifflin,  and  Company. 

Mammals 

Mammals.  —  Dogs  and  cats,  sheep  and  pigs,  horses  and  cows, 
all  of  our  domestic  animals  (and  man  himself),  have  characters  of 
structure  which  cause  them  to  be  classed  as  the  type  of  vertebrate 


312  THE  VERTEBRATE  ANIMALS 

animal  known  as  mammals.  These  characters  are  the  possessions 
of  a  hairy  covering,  of  lungs,  and  warm  blood.  They  bear  young 
developed  to  a  form  similar  to  their  own,^  and  nurse  them  with 
milk  secreted  by  glands  known  as  the  mammary  glands;  hence 
the  term  ''  mammal." 

Instincts.  —  Mammals  are  considered  the  highest  of  vertebrate 
animals,  not  only  because  of  their  compUcated  structure,  but  be- 
cause their  instincts  are  so  well  developed.  Monkeys  certainly 
seem  to  have  many  of  the  mental  attributes  of  man. 

Professor  Thorndike  of  Columbia  University  sums  up  their  habits 
of  learning  as  follows  :  — 

"  In  their  method  of  learning,  although  monkeys  do  not  reach  the 
human  stage  of  a  rich  life  of  ideas,  yet  they  carry  the  animal  method  of 
learning,  by  the  selection  of  impulses  and  association  of  them  with  differ- 
ent sense-impressions,  to  a  point  beyond  that  reached  by  any  other  of 
the  lower  animals.  In  this,  too,  they  resemble  man ;  for  he  differs  from 
the  lower  animals  not  only  in  the  possession  of  a  new  sort  of  intelligence, 
but  also  in  the  tremendous  extension  of  that  sort  which  he  has  in  common 
with  them.  A  fish  learns  slowly  a  few  simple  habits.  Man  learns  quickly 
an  infinitude  of  habits  that  may  be  highly  complex.  Dogs  and  cats  learn 
more  than  the  fish,  while  monkeys  learn  more  than  they.  In  the  number 
of  things  he  learns,  the  complex  habits  he  can  form,  the  variety  of  lines 
along  which  he  can  learn  them,  and  in  their  permanence  when  once  formed, 
the  monkey  justifies  his  inclusion  with  man  in  a  separate  mental  genus." 

Adaptations  in  Mammalia.  —  Of  the  thirty-five  hundred  species, 
most  inhabit  continents ;  few  species  are  found  on  different  islands, 
and  some,  as  the  whale,  inhabit  the  ocean.  They  vary  in  size  from 
the  whale  and  the  elephant  to  tiny  shrew  mice  and  moles.  Adapta- 
tions to  different  habitat  and  methods  of  life  abound ;  the  seal  and 
whale  have  the  limbs  modified  into  flippers,  the  sloth  and  squirrel 
have  limbs  peculiarly  adapted  to  climbing,  while  the  bats-  have  the 
fore  limbs  modeled  for  flight. 

Carnivorous  Mammals.  —  As  the  word  ''  carnivorous  "  denotes, 
these  animals  are  to  a  large  extent  flesh  eaters.  In  a  wild  state 
they  hunt  their  prey,  which  is  caught  and  torn  with  the  aid  of 
well-developed  claws  and  long,  sharp  teeth.  These  teeth,  so  well 
developed  in  the  dog,  are  known  as  canine  teeth  or  dog  teeth.  All 
flesh-eating  mammals  are  wandering  hunters  in  a  state  of  nature ; 

1  With  the  exception  of  the  monotremes. 


THE   VERTEBRATE  ANIMALS 


313 


Skull  of  a  dog.     Notice  the  size  and  shape  of 
the  canine  teeth. 


many,  as  the  bear  and  lion,  have  homes  or  dens  to  which  they  retreat. 
Some  (for  example,  bears  and  raccoons)  live  at  least  part  of  the  time 
upon  berries  and  fruit.  Seals,  sea  lions,  and  walruses  are  adapted 
to  a  life  in  the  water. 
Especially  in  the  seals,  the 
hind  limbs  are  almost  use- 
less on  land.  Some  of  the 
fur  bearers,  as  the  otter 
and  mink,  lead  a  partially 
aquatic  life.  Others  in  this 
great  group  prefer  regions 
of  comparative  dryness,  as 
the  inhabitants  of  the 
South  African  belt.  A  few 
have  come  to  live  most  of 
their  time  in  the  trees,  the  raccoon  being  an  example.  Many 
have  adaptations  for  food  getting  and  escape  from  enemies;  the 
seasonal  change  in  color  of  the  weasel  is  an  example  of  an  adapta- 
tion which  serves  both  of  the  above  purposes.  This  is  only  one 
of  hundreds  of  others  that  might  be  mentioned. 

Economic  Importance.  —  The  Carnivora  as  a  group  are  of  much 
economic  importance  as  the  source  of  most  of  our  fur.     The  fur  seal 

fisheries  alone  amount  to  many 
millions  of  dollars  annually. 
Otters,  skunks,  sables,  weasels, 
iind  minks  are  of  considerable 
importance  as  fur  producers. 
Our  domestic  cats  (particularly 
deserted  cats)  are  such  factors  in 
the  extermination  of  our  native 
birds  that  their  place  as  house 
pets  is  seriously  questioned 
by  some  people.  In  India  tigers,  and  in  Africa  lions,  are  man- 
eating  in  certain  localities,  and  in  our  own  country  wolves, 
pumas,  and  wild  cats  do  some  damage. 

Rodents.  —  Mammals  known  as  rodents  have  the  teeth  so 
modified  that  on  the  upper  and  lower  jaw  two  prominent  incisor 
teeth  can  be  used  for  gnawing.     These  teeth  keep  their  chisel-like 


The  Calilorma  soa  iion  [Zniophu.s  califor- 
nianus).  Photographed  in  the  Philadel- 
phia Zoological  Gardens  by  Davison. 


314 


THE  VERTEBRATE  ANIMALS 


Skull  of  a  porcupine,  a  rodent.  Notice  the  large 
overlapping  incisor  teeth.  Compare  them  with  the 
teeth  of  a  dog  (see  page  313). 


edge  because  the  back  part  of  the  teeth  is  softer  and  wears  away- 
more  rapidly.  The  canine  or  dog  teeth  are  lacking.  We  are 
all  familiar  with  the  destructive  gnawing  qualities  of  one  of  the 

commonest  of  all  ro- 
dents, the  rat.  The 
common  brown  rat  is  an 
example  of  a  mammal, 
harmful  to  civilized 
man,  which  has  fol- 
m,'^^  ^  ^HVS^^^I^HHHi  lowed  in  his  footsteps 
Ik  ^HBh^HHBO^I     ^^^    over   the    world. 

HL  ^^^^^B^^J^^H     Starting  from  China,  it 

am  ^^JBHH     spread    to    eastern 

Europe,  thence  to  west- 
ern Europe,  and  in  1775 
it  had  obtained  a  lodg- 
ment in  this  country. 
In  seventy-five  years  it 
reached  the  Pacific  coast,  and  is  now  fairly  common  all  over  the 
United  States,  being  one  of  the  most  prolific  of  all  mammals.  A 
determined  effort  is  now  being  made  to  exterminate  this  pest  be- 
cause of  its  connection  with  bubonic  plague. 

Although  most  rodents  may  be 
considered  as  pests  (as  the  rat  and 
mouse),  others  are  of  use  to  man. 
Some  of  this  order  furnish  food  to 
man,  as  the  rabbit,  hares,  and  squir- 
rels. Rabbits,  although  rapid 
breeders,  are  kept  in  check  in  most 
parts  of  this  country  by  their  nat- 
ural enemies,  birds  of  prey,  and 
flesh-eating  mammals.  But  in 
Australia,  where  they  were  intro- 
duced by  man,  they  have  become 
so  numerous  as  to  require  govern- 
ment action  in  the  form  of  a  bounty  for  their  destruction.  Thou- 
sands of  sheep  are  starved  to  death  each  year  because  rabbits  eat 
up  their  pasturage.     The  fur  of  the  beaver,  one  of  the  largest  of 


Beaver  (Castor  canadensis).  North 
America.  Copyright,  1900,  by  A. 
Rad  cliff e  Dugmore. 


THE  VERTEBRATE  ANIMALS 


315 


this  order,  is  of  considerable  value,  as  are  the  coats  of  several 

other  rodents.     The  fur  of  the  rabbit  is  used  in  the  manufacture 

of  felt  hats.     The  quills  of  the  porcupines  (greatly  developed  and 

stiffened     hairs)     have     a 

slight  commercial  value. 
Ungulates:     Hoofed 

Mammals.  —  This    group 

includes  the  domesticated 

animals,  as  the  horse,  cow, 

sheep,  and  pig.     A  group 

of  animals  which  originally 

roamed  wild,  many  species 

eventually  came  under  the 

subjugating     influence    of 

man.     Now   they  form   a 

source    of    the    world's 

wealth,  and  are  an  impor- 
tant part  of  the  wealth  of 

the  United  States. 
The  order  of  ungulates 

is  a  very  large  one.     It  is  characterized  by  the  fact  that  the  nails 

have  grown  down  to  become  thickened  as  hoofs.     In  some  cases 

only  two  (the  third  and 
fourth)  toes  are  largely 
developed.  Such  animals 
have  a  cleft  hoof,  as  in  the 
ox,  deer,  sheep,  and  pigs. 
These  form  the  even-toed 
ungulates.  The  deer  fam- 
ily  are  the  largest  in 
number  of  species  and 
individuals  among  our 
native  forms,  and  in  fact 
the  world  over.  Among 
them     are    the     common 

Virginia  deer  of  the  Eastern  states,  the  white-tailed  deer  of  our 

Adirondack  forests.     The  bison,  or  buffalo,  is  nearly  related  to 

the  deer  and  wild  cattle.     Formerly  bisons  existed  in  enormous 


Virginia    door.     From   photograph   loaned   by 
the  American  Museum  of  Natural  History. 


1  h('  bisou. 


316  THE  VERTEBRATE  ANIMALS 

numbers  on  our  Western  plains.  They  were  hunted  by  whites 
and  Indians  for  the  hides  and  tongues  only,  and  thousands  of 
carcasses  were  left  to  rot  after  a  hunt.  They  are  now  almost 
extinct. 

Geologic  History  of  the  Horse.  —  In  some  ungulates  the  middle 
toe  of  the  foot  has  become  largely  developed,  ^vith  the  result  that 
the  animal  stands  on  it.     Such  are  the  zebra  and  the  horse. 

We  have,  from  time  to  time,  made  reference  to  the  fact 
that  certain  forms  of  life,  now  almost  extinct,  flourished  on 
the  earth  in  former  geologic  periods.  It  is  interesting  to  note 
that  America  was  the  original  home  of  the  horse,  although  at  the 
time  of  the  earliest  explorers  the  horse  was  unknown  here,  the 
wild  horse  of  the  Western  plains  having  arisen  from  horses 
introduced  by  the  Spaniards.  Long  ages  ago,  the  first  ances- 
tors of  the  horse  were  probably  little  animals  about  the  size 
of  a  fox.  The  earliest  horse  we  have  knowledge  of  had  four  toes 
on  the  fore  and  three  toes  on  the  hind  feet.  Thousands  of  years 
later  we  find  a  larger  horse,  the  size  of  a  sheep,  with  a  three-toed 
foot.  By  gradual  changes,  caused  by  the  tendency  of  the  animals 
to  vary  and  by  the  action  of  the  surroundings  upon  the  animal 
in  preserving  these  variations,  there  was  eventually  produced  our 
present  horse,  an  animal  with  legs  adapted  for  rapid  locomotion, 
with  feet  particularly  fitted  for  the  life  in  open  fields,  and  with 
teeth  which  serve  well  to  seize  and  grind  herbage. 

Domestication  of  Animals;  Breeding  by  Selection.  —  The 
horse,  which  for  some  reason  disappeared  in  this  country,  con- 
tinued to  exist  in  Europe,  and  man,  emerging  from  his  early  savage 
condition,  began  to  make  use  of  the  animal.  We  know  the  horse 
was  domesticated  in  early  Biblical  times,  and  that  he  soon  became 
one  of  man's  most  valued  servants.  In  more  recent  times,  man 
has  begun  to  artificially  change  the  horse  by  breeding  for  certain 
desired  characteristics. 

To  do  this,  the  horses  which  have  varied  so  as  to  show  the  char- 
acters desired  by  the  breeder  are  selected  and  bred  together.  The 
young  from  these  animals  are  likely  to  be  like  the  parents  and,  be- 
cause of  the  tendency  of  animals  to  vary,  will  be  even  more  likely 
to  show  the  characters  the  breeder  desires  than  their  parents.  If 
this  process  is  repeated  for  several  generations,  it  will  be  seen  that 


THE  VERTEBRATE  ANIMALS 


317 


man,  by  artificial  selection,  might  have  considerably  modified  the 
type  of  horse  with  which  he  started.  In  this  mamier  have  been 
estabhshed  and  improved  the  various  types  of  horses  famihar 
to  us  as  draft  horses,  coaches  and  hackneys,  and  the  trotters.  In 
a  similar  manner  have  been  obtained  the  various  breeds  of  cattle, 
sheep,  swine,  etc. 

It  is  needless  to  say  that  all  the  various  domesticated  animals 
have  been  tremendously  changed  in  a  similar  manner  since  civilized 
man  has  come  to  live  on  the  earth.  When  we  realize  the  very 
great  amount  of  money  invested  in  domesticated  animals;  that 
there  are  over  60,000,000  each  of  sheep,  cattle,  and  swine  and 
over  20,000,000  horses  owned  in  this  country,  then  we  may  see 
how  very  important  a  part  the  domestic  animals  play  in  our  lives. 

Other  Orders  of  Mammals.  —  The  lowest  are  the  monotremes,  animals 
which  lay  eggs  like  the  ])irds,  although   they  are  provided  with  hairy 

covering   like    other    mammals. 

Such   are  the  Australian   spiny 
anteater  and  the  duck  mole. 

All  other  mammals  bring  forth 
their  young  developed  to  a  form 
similar  to  their  own.  The  kan- 
garoos and  opossum,  however, 
are  provided  with  a  pouch  on 
the  ventral  side  of  the  body  in 
which  the  very  immature,  bhnd, 
and  helpless  young  are  nour- 
ished until  they  are  able  to  care 
for  themselves.  These  pouched 
animals  are  called  marsupials. 

The  other  mammals,  in  which  the  young  are  born  able  to  care  for 
themselves,  and  have  the  form  of  the  adult,  may  be  briefly  classified  as 
follows :  — 


Virginia  opossum.     Photograph,  one  eighth 
natural  size,  by  N.  F.  Davis. 


Character 

Edentates  Toothless  or  with  very  simple 
teeth 

Rodents  Incisor  teeth,  chisel-shaped,  usu- 

ally two  above  and  two 
below 

Cetaceans  Adapted  to  marine  life,  teeth  of 
whales  sometimes  platelike 


Examples 

Anteater 
Sloth 
Armadillo 
Beaver,  rat 
Porcupine,  rabbit 
Squirrels 
Whales 
Porpoise 


318 


TPIE   VERTEBRATE  ANIMALS 


Ungulates       Hoofs,  teeth,  adapted  for  grinding     (a) 


(b) 


Carnivora  Long  canine  teeth,  sharp  and  long 
claws,  usually  aggressively 
colored 


Chiroptera      Fore  limbs  adapted  to  flight,  teeth 

pointed 
Primates         Erect  or  nearly  so,  fore  appendage 

provided  with  hand 

Reference  Books 
elementary 


Odd-toed 

Horse 

Rhinoceros 

Tapir 

Even-toed 

Ox 

Pig 

Sheep 

Deer 

Dogs 

Cats 

Lions 

Bears,  etc. 

Seals  and  sea 

Bat 

Monkeys 

Apes 

Man 


lions 


Sharpe,  A  Laboratory  Manual  for  the  Solution  of  Problems  in  Biology.    American 

Book  Company. 
Hodge,  Nature  Study  and  Life.     Chap.  III.     Ginn  and  Company. 
Ingersoll,  Wild  Neighbors.     The  Macmillan  Company. 
Lucas,  Animals  of  the  Past.     McClure,  Phillips,  and  Company. 
Matthew,   The  Evolution  of  the  Horse,  Guide  Leaflet  No.  9,  American  Museum  of 

Natural  History. 
Stone  and  Cram,  American  Animals.     Doubleday,  Page,  and  Company. 
Wright,  Four-footed  Americans.     The  Macmillan  Company. 


ADVANCED 


Flower,  The  Horse.     D.  Appleton  and  Company. 

Kingsley,  Riverside  Natural  History.     Houghton,  Mifflin,  and  Company. 
Schaler,  Domesticated  Animals,  their  Relation  to  Man  and  to  His  Advancement  in 
Civilization.    Charles  Scribner's  Sons. 


XXIII.    MAN,  A  MAMMAL 

jproblein  XLI.    A  study  of  man  as  a  vertebrate  compared 
with  tJiefrog'    {Laboratory  Manual,  Prob.  XLI.) 
(a)  Comparison  of  body  covering, 
(,b)  TJw  study  of  muscles. 
(c)  Adaptations  in  the  skeleton, 
id)  Jfervous  system. 

Man's  Place  in  Nature.  —  Although  we  know  that  man  is  sepa- 
rated mentally  by  a  wide  gap  from  all  other  animals,  in  our  study 
of  physiology  we  must  ask  where  we  are  to  place  man.  If  we 
attempt  to  classify  man,  we  see  at  once  he  must  be  placed  with 
the  vertebrate  animals  because  of  his  possession  of  a  vertebral 
column.  Evidently,  too,  he  is  a  manamal,  because  the  young  are 
nourished  by  milk  secreted  by  the  mother  and  because  his  body 
has  at  least  a  partial  covering  of  hair.  Anatomically  we  find  that 
we  must  place  man  with  the  apelike  mammals,  because  of  thdse 
numerous  points  of  structural  likeness.  The  group  of  mammals 
which  includes  the  monkeys,  apes,  and  man  we  call  the  primates. 

Although  anatomically  there  is  a  greater  difference  between' 
the  lowest  type  of  monkey  and  Lhe  highest  type  of  ape  than  there 
is  between  the  highest  type  of  ape  and  the  lowest  savage,  yet  there 
is  an  immense  mental  gap. 

Undoubtedly  there  once  lived  upon  the  earth  races  of  men  who 
were  much  lower  in  their  mental  organization  than  the  present 
inhabitants. 

Evolution  of  Man.  —  If  we  follow  the  early  history  of  man  upon 
the  earth,  we  find  that  at  first  he  must  have  been  Uttle  better  than 
one  of  the  lower  animals.  He  was  a  nomad,  wandering  from  place 
to  place,  living  upon  whatever  living  things  he  could  kill  with  his 
hands.  Gradually  he  must  have  learned  to  use  weapons,  and  thus 
kill  his  prey,  first  using  rough  stone  implements  for  this  purpose. 
As  man  became  more  civihzed,  implements  of  bronze  and  of  iron 

319 


320  MAN,  A  MAMMAL 

were  used.  About  this  time  the  subjugation  and  domestication  of 
animals  began  to  take  place.  Man  then  began  to  cultivate  the 
fields,  and  to  have  a  fixed  place  of  abode  other  than  a  cave.  The 
beginnings  of  civilization  were  long  ago,  but  even  to-day  the  earth 
is  not  entirely  civilized. 

The  Races  of  Man.  —  At  the  present  time  there  exist  upon  the 
earth  five  races  or  varieties  of  man,  each  very  different  from  the 
other  in  instincts,  social  customs,  and,  to  an  extent,  in  structure. 
These  are  the  Ethiopian  or  negro  type,  originating  in  Africa;  the 
Malay  or  brown  race,  from  the  islands  of  the  Pacific;  the  Amer- 
ican Indian;  the  Mongolian  or  yellow  race,  including  the  natives 
of  China,  Japan,  and  the  Eskimos;  and,  finally,  the  highest  type 
of  all,  the  Caucasians,  represented  by  the  civilized  white  in- 
habitants  of  Europe  and  America. 

The  Human  Body  a  Machine.  —  In  all  animals,  and  the  human 
animal  is  no  exception,  the  body  has  been  likened  to  a  ma- 
chine in  that  it  turns  over  the  latent  or  potential  energy  stored 
up  in  food  into  kinetic  energy  (mechanical  work  and  heat),  which  is 
manifested  when  we  perform  work.  One  great  difference  exists 
between  an  engine  and  the  human  body.  The  engine  uses  fuel 
unlike  the  substance  out  of  which  it  is  made.  The  human  body, 
on  the  other  hand,  uses  for  fuel  the  same  substances  out  of  which 
it  is  formed ;  it  may,  indeed,  use  part  of  its  own  substance  for  food. 
It  must  as  well  do  more  than  purely  mechanical  work.  The  human 
organism  must  be  so  delicately  adjusted  to  its  surroundings  that 
it  will  react  in  a  ready  manner  to  stimuli  from  without ;  it  must 
be  able  to  utilize  its  fuel  (food)  in  the  most  economical  manner; 
it  must  be  fitted  with  machinery  for  transforming  the  energy  re- 
ceived from  food  into  various  kinds  of  work;  it  must  properly 
provide  the  machine  with  oxygen  so  that  the  fuel  will  be  oxidized, 
and  the  products  of  oxidation  must  be  carried  away,  as  well  as 
other  waste  materials  which  might  harm  the  effectiveness  of  the 
machine.  Most  important  of  all,  the  human  machine  must  be  able 
to  repair  itself. 

In  order  to  understand  better  this  complicated  machine,  the 
human  body,  let  us  examine  the  structure  of  its  parts  and  thus 
get  a  better  idea  of  the  interrelation  of  these  parts  and  of  their 
functions. 


MAN,  A  MAMMAL 


321 


Structure  of  the  Skin.  —  In  man,  the  outer  covering  of  the 
skin  is  composed  of  two  layers.  The  outer  part  (called  the 
epidermis)  is  composed  largely  of  flattened  dead  cells.  It  is  part 
of  this  layer  that  peels  off  after  sunburn,  or  that  separates  from 
the  inner  part  of  the  epidermis  when  a  water  blister  is  formed. 
The  inner  cells  of  the  epidermis  are  provided  with  more  or 
less  pigment  or  coloring  matter.  It  is  to  the  varying  quantity 
of  this  pigment  that  the  light  or  dark  complexion  is  due. 
The  inmost  layer  of  the  epidermis  is  made  up  of  small  cells  which 
are  constantly  dividing  to  form  new  cells  to  take  the  place  of 
those  in  the  outer  layer  which  are  lost. 


Suheutaneo»»  Infer  of 
connective  tUtue  and  /at 


Diagram  of  a  section  of  the  skin.    (Highly  magnified.) 


The  dermis,  or  inner  layer,  is  largely  composed  of  connective  tissue 
filled  with  a  network  of  blood  vessels  and  nerves.  This  layer  con- 
tains the  sweat  glands,  some  of  the  most  important  glands  in  the 
body.  Other  organs  connected  with  the  nervous  system,  and  called 
the  tactile  corpuscles,  cause  this  part  of  the  skin  to  be  sensitive  to 
touch. 

Nails  and  Hairs.  —  Nails  are  a  development  from  the  horny 
layer  of  the  epidermis.  A  hair  is  also  an  outgrowth  of  the 
horny  layer,  although  it  is  formed  in  a  deep  pit  or  depression  in 
the  dermis ;  this  pit  is  called  the  hair  follicle. 

HUNT.  ES.  BIO. — 21 


322 


MAN,  A  MAMMAL 


The  Glands  of  the  Skin.  —  Scattered  through  the  dermis,  and 
usually  connected  with  the  hair  follicles,  are  tiny  oil-secreting 
glands,  the  sebaceous  glands.  The  function  of  the  sebaceous  gland 
is  to  keep  the  hair  and  surface  of  the  skin  soft.  The  other  glands, 
known  as  sweat  glands,  are  to  be  found  in  profusion,  over  2,500,000 
being  present  in  the  skin  of  a  normal  man.  These  glands  carry 
off  certain  wastes  from  the  blood  in  the  water  they  pass  off. 
Thus  the  skin  not  only  protects  the  body,  but  also  serves  as 
an  excretory  organ.  Its  most  important  function,  however,  is 
the  regulation  of  the  h^t  of  the  body.  How  it  does  this,  we 
shall  learn  later.     (See  (phapter  XXVII.) 

Connective  Tissue.  —  The  layer  immediately  beneath  the  der- 
mis is  known  as  the  subcutaneous  layer.  It  is  an  important 
storage  place  for  fat.  Underneath  this  layer  we  find  a  mass  of 
flesh  or  muscle.  Intermixed  with  this  is  a  considerable  amount 
of  fat.  The  fat,  muscle,  —  in  fact,  all  the  tissues  in  the  body,  — 
are  held  together  by  fibrous  threads  called  connective  tissue. 
Muscles  and  Movement.  —  We  are  all  aware  that  motion  in  any 
of  the  higher  animals  is  caused  by  the  action  of 
the  muscles.  These  contract  to  cause  move- 
ment. In  man  and  the  other  vertebrate  ani- 
mals, the  muscles  are  almost  always  fastened 
to  bones,  which,  acting  as  levers,  give  wide 
range  of  motion. 

Arrangement  of  Voluntary  Muscles  in  the 
Human  Body.  —  Muscles  are  usually  placed 
in  pairs;  one,  called  the  extensor,  serves  to 
straighten  the  joint;  the  other,  the  flexor, 
bends  the  joint.  Locate,  by  means  of  feeling 
the  muscles  when  expanded  and  when  con- 
tracted, the  extensors  and  flexors  in  your 
own  arm.  Use  the  leg  of  a  frog  to  deter- 
mine which  muscles  are  extensors  and  which 
flexors  (see  the  Figure).  This  paired  arrange- 
Muscles  of  the  left  leg  of  ment  of  muscles  is  of  obvious  importance,  a 
the  frog ;  h,  M.  biceps ;  flexor  muscle  balancing  the  action  of  an  ex- 
L.^M.temImembmn-  ^^usor  ou  the  other  side  of  the  joint.  The 
osus ;  tr,  M.  triceps.      end  of  the  muscle  that  has  the  wider  move- 


MAN,  A  MAMMAL 


323 


ment  in  a  contraction  is  called 
the  insertion;  the  part  that  moves 
least  is  the  origin. 

Microscopic  Structure  of  Volun- 
tary Muscle,  —  With  a  sharp  pair  of 
scissors  cut  through  a  muscle  at  right 
angles  to  the  long  axis ;  examina- 
tion will  show  that  it  is  composed  of 
a  number  of  bundles  of  fibers.  These 
fibers  are  held  together  by  a  sheath 
of  connective  tissue.  Each  of  these 
bundles  may  be  separated  into  smaller 
ones.  If  we  continue  this  so  as  to 
separate  into  the  smallest  possible  bits 
that  can  be  seen  with  the  naked  eye, 
and  then  examine  such  a  tiny  portion 
under  the  compound  microscope,  it 
will  present  somewhat  the  appearance 
shown  in  the  Figure.  The  muscle  is 
seen  to  be  made  up  of  a  number  of  tiny 
threads  which  lie  side  by  side,  held 
together  by  the  sheath.  Muscles, 
then,  are  bundles  of  long  fibers.  In 
man,  muscles  which  are  under  the 
control  of  the  will  have  a   striated 

appearance,  while    those  which    are    involuntary  are    unstriated.     Both 
kinds  are  supplied  with  nerves,  which  control  them  (see  Figures). 


A  bit  of  voluntary  muscle  fiber,  showing 
the  cross  striations  as  seen  under  the 
microscope.     (Highly  magnified.) 


The  delicate  endings  of  nerves  in  vol- 
untaiy  muscle.    (Highly  magnified.) 


Muscle  Tissue  and  its  Uses. — 
Muscles  evidently  form  a  large 
part  of  the  body,  in  man,  nearly 
half  the  body  weight  being  muscle. 
Nearly  every  muscle  in  the  human 
body  is  attached  to  a  bone  either 
at  one  or  at  both  ends.  Move- 
ment is  performed  by  means  of  the 
muscles,  leverage  being  obtained 
by  means  of  their  attachment  to 
the  bones.  Movement  is,  indeed, 
the  chief  function  of  muscles.  In 
the  human  body  there  are  over 


324  MAN,  A  MAMMAL 

five  hundred  muscles,  varying  from  one  smaller  than  a  pinhead  to 
a  band  almost  two  feet  in  length.  Every  movement  of  the  body, 
be  it  merely  a  change  of  expression  or  change  in  the  pitch  of  the 
voice,  directly  results  from  contraction  of  a  muscle.  Muscles  also 
give  form  to  the  body,  and  are  useful  in  protecting  the  delicate 
organs  and  large  blood  vessels  within  them. 

Muscles  and  the  Skeleton.  —  Muscles  would  be  of  httle  use  to 
animals  if  they  were  not  attached  to  hard  parts  of  the  body  which 
serve  as  levers.  In  many  invertebrate  animals  (for  example, 
crustaceans,  insects,  and  mollusks),  the  muscles  are  attached  to  the 
exoskeleton.     In  man  they  are  attached  to  the  endoskeleton. 

In  the  hind  leg  of  the  frog,  if  we  cut  through  the  muscles  of  the  thigh 
to  the  bone,  we  may  make  out  exactly  how  and  where  the  muscles  of 
the  thigh  are  attached  to  the  bone.  Moving  the  leg 
in  as  many  different  directions  as  possible,  we  notice 
that  it  may  be  flexed  or  bent ;  that  it  may  be  ex- 
tended to  its  original  position  ;  that  it  may  be  moved 
to  and  from  the  midline  of  the  body ;  that,  with  the 
knee  held  stiff,  the  whole  limb  may  be  made  to  de- 
scribe the  arc  of  a  circle.^ 

These  same  movements  are  possible  in  the  leg  of 
a  man.  This  movement  between  bones  is  obtained 
by  means  of  joints.  If,  in  the  frog,  we  carefully 
separate  the  muscles  of  the  thigh  to  the  bone,  we 
find  that  they  are  attached  to  the  bone  by  white, 
glistening  tendons.  Careful  examination  shows  that 
the  bones  themselves  are  held  together  by  very  tough 
Hinge  joint,  showing     ^j^j^^  ^^^^^  ^^  ^^^^^ .    ^^^^^  ^^^  ^^^  ligaments.     We 

Sndon  (6)   ^""^  '*^     ^^^'  ^^^'  ^^^*  ^^®   ®^^   ^^   ^^®  ^^^^®  *^^^  ^^^®  ^*^ 
into  a  socket  in  the  hip  bone  or  pelvic  arch.     It  is 

thus  easy  to  see  how  such  free  movement  is  obtained  in  the  leg. 

Levers  in  the  Body.  —  It  is  evident  that  movement  of  a  joint  is  caused 
by  muscles  which  act  in  cooperation  with  the  bones  to  which  they  are  at- 
tached ;  the  latter  thus  form  true  levers.  A  lever  is  a  structure  by  which 
either  greater  work  power  or  greater  range  of  motion  is  obtained.  In 
this  apparatus,  the  lever  works  against  a  fixed  point,  the  fulcrum,  in  order 
to  raise  a  certain  weight.  A  seesaw  is  a  lever ;  here  the  fulcrum  is  in  the 
middle,  the  weight  is  at  one  end,  and  the  power  to  lift  the  weight  is  ap- 
plied at  the  other  end.  There  are  three  classes  of  levers,  named  accord- 
ing to  the  position  of  the  fulcrum. 

In  the  first  class,  the  fulcrum  lies  between  the  weight  and  the  power ; 

1  At  this  point  demonstration  with  a  human  skeleton  should  be  made. 


MAN,  A  MAMMAL 


326 


the  seesaw  is  an  example  of  this.  The  l)est  example  in  the  human  body  of 
a  lever  of  the  first  class  is  seen  when  the  head  nods.  Here  the  fulcrum  is 
the  vertebra  known  as  the  atlas;  the  power  is  the  muscles  of  the  neck 
attached  to  the  back  of  the  skull  and  to  the  spine ;  the  weight  is  the  front 
part  of  the  head.  When  one  keeps  the  head  erect,  this  lever  is  used; 
the  nodding  head  when  one  is  napping  shows  this  plainly. 


\ 


^ 


.^  B  C 

Three  classes  of  levers.    A,  a  lever  of  the  first  class;  B,  a  lever  of  the  second  class; 
C,  a  lever  of  the  third  class.     (See  text.) 


A  lever  of  the  second  class  has  the  fulcrum  at  one  end,  and  the  weight 
between  it  and  the  power ;  when  we  rise  on  our  toes,  we  use  this  kind  of 
lever. 

In  a  lever  of  the  third  class,  the  fulcrum  is  at  one  end,  with  the  power 
between  it  and  the  weight.  This  is  the  kind  of  lever  seen  most  frequently 
in  the  human  body.  The  flexing  (drawing  up)  of  the  lower  leg  or  the  fore- 
arm is  an  example  of  the  use  of  this  kind  of  lever.  In  such  a  lever,  a  wide 
range  of  movement  is  obtained. 

General  Structure  and  Uses  of  the  Skeleton.  —  Evidently  bones 
form  a  framework  to  which  muscles  are  attached;  thus  they  are 
used  as  levers  for  pur- 
poses of  movement. 
Second,  they  give  pro- 
tection to  delicate  or- 
gans ;  they  form  a  case 
around  the  brain  and 
spinal  cord ;  as  ribs 
they  protect  the  or- 
gans in  the  body 
cavity.  Third,  they 
give  rigidity  and  form 

to  the  body.  The  skeleton  of  a  dog;  a  typical  mammal. 


326 


MAN,  A  MAMMAL 


The  skeleton  of  vertebrate  animals  consists  of  two  distinct 
regions  :  a  vertebral  column  of  backbone  which,  with  the  skull,  forms 

the  dxial  skeleton;  and  the  parts 
attached  to  this  main  axis,  the  ap- 
pendicular skeleton  (the  append- 
ages). All  skeletons  of  vertebrates 
have  the  same  general  regions,  the 
size  and  shape  of  the  bones  in  these 
regions  differing  somewhat  in  each 
kind  of  animal. 

In  the  axial  skeleton  of  the  frog, 
as  well  as  in  man,  the  vertebral 
column  is  made  up  of  a  number  of 
bones  of  irregular  shape,  which  fit 
more  or  less  closely  into  each  other. 
These  bones  are  called  vertehroe. 
Notice  that  the  vertebrae  possess 
long  processes  to  which  muscles  of 
the  back  are  attached.  Certain  of 
the  vertebrae  bear  ribs  (arched,  flat 
bones) ,  the  special  function  of  which 
is  to  protect  the  organs  of  the  upper 
body  cavity. 

Adaptations  in  the  Vertebral  Col- 
umn. —  The  vertebral  column  in 
man  is  made  up  of  many  separate 
pieces  of  bone :  thirty-three  in  a 
child;  twenty-six  in  the  adult, 
several  bones  in  the  region  of  the 
pelvis  later  growing  together.  Each 
vertebra  presents  the  general  form 
of  a  body  or  centrum  of  bone  and 
a  bony  arch  with  seven  projections ; 
in  this  arch  runs  the  spinal  cord. 
The  surface  of  the  centrum  and 
those  parts  of  the  vertebrae,  each  of 
which  fits  into  its  next  neighbor,  are  covered  with  pads  of  cartilage. 
Two  of  the  processes  in  each  vertebra  project  forward  and  two  back- 


Skeleton  of  man  :  CR,  cranium ; 
CL,  clavicle;  ST,  sternum;  SC, 
scapula;  H,  humerus;  VC,  ver- 
tebral column ;  R,  radius ;  U,  ulna ; 
P,  pelvic  girdle ;  C,  carpals ;  MC, 
metacarpals;  Ph,  phalanges;  F, 
femur ;  Fi,  fibula ;  T,  tibia ;  Tar, 
tarsals;  MT,  metatarsals. 


MAN,  A  MAMMAL 


327 


ward ;  these  form  articulations  or  joints  with  the  neighboring  verte- 
brae. Of  the  other  processes,  one  projects  dorsally  and  two  project 
laterally ;  these  give  attachment  to  the  muscles  of  the  back.  The 
two  vertebrae  directly  beneath  the  head  are  modified  so  as  to  permit 
the  skull  to  rest  in  the  upper  one ;  this  articulates  freely  with  the 
second  vertebra,  thus  permitting  of  the  nodding  and  turning  move- 
ments of  the  head.  Besides  these  individual  adaptations,  the 
vertebral  column,  as  a  whole,  is  peculiarly  adapted  to  protect  the 
brain  from  jar;  this  is  seen  in  the  double  bend  of  the  vertebral 
column  and  the  pads  of  cartilage  between  the  individual  vertebrae. 
The  whole  column  of  vertebrae  joined 
each  to  the  other  supports  the  weight 
of  the  body.  The  largest  vertebrie 
at  the  base  are  joined  to  the  huge 
pelvic  bones  for  the  better  support 
of  the  body  above.  That  part  of  the 
vertebral  column  of  man  which  bears 
the  ribs  is  known  as  the  thoracic  re- 
gion. The  ribs,  twelve  in  number,  are 
long,  curved  bones  which  combine 
lightness  with  strength;  joined  by 
elastic  cartilage  to  the  sternum  in 
front  and  to  the  vertebrae  behind,  they  form  a  wonderful  pro- 
tection to  the  organs  in  the  thoracic  cavity,  and  yet  allow  free 
movement  in  breathing. 

The  Appendages.  —  The  parts  of  the  skeleton  to  which  the 
bones  of  the  anterior  and  posterior  appendages  are  attached  are 
respectively  known  as  the  pectoral  girdle  (from  which  hangs  the 
arm)  and  the  pelvic  girdle  (which  joins  the  leg  bones  to  the 
axial  skeleton). 

The  bones  of  the  appendages  attached  to  the  pectoral  and 
pelvic  girdles  are  adapted  peculiarly  to  locomotion  and  sup- 
port ;  for  this  purpose  the  bones  are  long  and  strong,  hinged  by 
very  flexible  joints.  The  latter  are  especially  free  in  the  hand 
to  allow  for  grasping.  In  the  leg,  where  weight  must  be  supported 
as  well  as  carried,  the  bones  are  bound  more  firmly  to  the  axial 
skeleton.  The  bones  of  the  foot  are  so  arranged  that  a  springy 
arch  is  formed  which  aids  greatly  in  locomotion. 


Vertebra,  showing  attachment  of 
ribs ;  C,  centrum  ;  R,  riba ;  SP, 
spinous  process. 


328 


MAN,  A  MAMMAL 


The  skull:  F.,  frontal  bone;  P.,  parietal  bone; 
T.,  temporal  bone ;  SP.,  sphenoid  bone;  O.,  occi- 
pital bone;  U.J.,  superior  maxillary  (upper 
jaw)  bone  ;  L.J.,  inferior  maxillary  (lower  jaw) 
bone. 


The  Human  Skull.  —  The  skull  shows  wonderful  adaptations  for  its 
varied  functions.  The  brain  case  is  compactly  built,  its  arched  roof 
giving  strength.     The  eye  and  inner  ear  are  protected  in  sockets  of  bone. 

The  lower  jaw  works  upon  a 
hinge,  and  furnishes  attach- 
ment for  strong  muscles  which 
move  the  jaw. 

The  skeleton,  besides  the 
purposes  already  described, 
protects  certain  organs  in 
the  body  cavity  of  man. 

Other  Organs.  ^ — ^  We 
have  seen  that  a  body 
cavity  has  developed  in  all 
animals  which  are  more 
complex  than  the  baglike 
hydra,  and  that  a  food  tube 
has  come  to  lie  within  this 
space.  In  all  such  animals 
the  structures  which  have  to  do  with  digestion  and  absorption  of  food, 
most  of  the  structures  which  have  to  do  with  the  circulation  of  this 
food  and  of  the  blood,  and  organs  which  give  oxygen  to  the  blood, 
as  well  as  the  organs  of  excretion  and  of  reproduction,  lie  within 
the  body  cavity.     These  organs  we  shall  discuss  in  detail  later. 

Nerves.  —  Other  structures,  known  as  nerves,  are  found  in  prac- 
tically all  parts  of  the  body.  We  find  that  nerves  have  their  end- 
ings in  the  skin,  in  muscle,  and  in  the  cells  of  glands  in  various  parts 
of  the  body;  we  find  a  nerve  supply  to  the  heart,  lungs,  and 
other  structures  within  the  body  cavity.  The  most  important 
part  of  the  nervous  system  in  vertebrate  animals  lies  within  the 
cavity  formed  by  bones  making  up  the  skull  and  the  vertebral 
column.  This  central  nervous  system,  the  spinal  column  and 
the  hrain,  is  a  characteristic  of  the  vertebrate  animals. 

General  Functions  of  the  Nervous  System.  —  We  have  seen  that, 
in  the  simplest  of  animals,  one  cell  performs  the  functions  neces- 
sary to  its  existence.  In  the  more  complex  animals,  where  groups 
of  cells  form  tissues,  each  having  a  different  function,  a  nervous 
system  is  developed.     Thefundions  of  the  human  nervous  system  are  : 


MAN,   A  MAMMAL  329 

(1)  the  providing  of  man  with  sensation,  by  means  of  which  he  gets  in 
touch  with  the  world  about  him;  (2)  the  connection  of  organs  in  dif- 
ferent parts  of  the  body  so  that  they  act  as  a  united  and  harmonious 
whole;  (3)  the  giving  to  the  human  being  a  will,  a  provision  for  thought. 
Cooperation  in  word  and  deed  is  the  end  attained.  We  are  all 
familiar  with  examples  of  the  cooperation  of  organs.  You  see 
food ;  the  thought  comes  that  it  is  good  to  eat ;  you  reach  out,  take 
it,  raise  it  to  the  mouth ;  the  jaws  move  in  response  to  your  will ; 
the  food  is  chewed  and  swallowed ;  while  digestion  and  absorption 
of  the  food  are  taking  place,  the  nervous  s^'stem  is  still  in  control. 
The  nervous  system  also  regulates  pumping  of  blood  over  the  body, 
respiration,  secretion  of  glands,  and,  indeed,  every  bodily  function. 
Man  is  the  highest  of  all  animals  because  of  the  extreme  develop- 
ment of  the  nervous  system.  Man  is  the  thinking  animal,  and 
as  such  is  master  of  the  earth. 

Reference  Reading  for  This  and  Succeeding  Chapters  on  Hitman  Biology 

elementary 

Sharpe,  A  Laboratory  Manual  Jor  the  Solution  of  Problems  in  Biology.     American 

Book  Company. 
Davison,  The  Human  Body  and  Health.     American  Book  Company. 
Eddy,  General  Physiology.     American  Book  Company. 
Hall,  Elementary  Physiology.     American  Book  Company. 
Clodd,  Primer  of  Evolution.     Longmans,  Green,  and  Company. 
Clodd,  The  Story  of  Primitive  Man.     Longmans,  Green,  and  Company. 
Ritchie,  Human  Physiology.     Worid  Book  Company. 

advanced 

Halliburton,  Kirk^s  Handbook  of  Physiology.     P.  Blakiston's  Son  and  Company. 
Hough  and  Sedgwick,  The  Human  Mechanism.     Ginn  and  Company. 
Howell,  Physiology,  3d  edition.     W.  B.  Saunders  Company. 
Schafer,  Textbook  of  Physiology.     The  Macmillan  Company. 
Stewart,  Manuxil  of  Physiology.     W.  B.  Saunders  Company. 
Verworn,  General  Physiology.     The  Macmillan  Company. 


XXIV.    FOODS  AND  DIETARIES 

Problem  XLII.    A  study  of  food  values  and  diets.    (^Laboror- 
tory  Manual,  Proho  XLII.) 
{a)  Food  values  and  cost. 
(Jb)  JVutritive  values  as  compared  with  cost. 

(c)  The  family  dietary. 

(d)  Food  values. 

Why  we  need  Food.  —  We  have  already  defined  food  as  anything 
that  forms  material  for  the  growth  or  repair  of  the  body  of  a  plant  or 
animal,  or  that  furnishes  energy  for  it.  The  millions  of  cells  of  which 
the  body  is  composed  must  be  given  material  which  will  form  more 
living  matter  or  material  which  can  be  oxidized  to  release  energy 
when  muscle  cells  move,  or  gland  cells  secrete,  or  brain  cells  think. 
Food,  then,  not  only  furnishes  our  body  with  material  to  grow,  but 
also  gives  us  the  energy  we  expend  in  the  acts  of  walking,  running, 
breathing,  and  even  in  thinking. 

Nutrients.  —  Certain  nutrient  materials  form  the  basis  of  food  of 
both  plants  and  animals.  These  have  been  stated  to  be  proteids 
(such  as  lean  meat,  eggs,  the  gluten  of  bread),  carbohydrates 
(starches,  sugars,  gums,  etc.),  fats  and  oils  (both  animal  and  vege- 
table), and  mineral  matter  and  water.  The  parts  of  the  human 
body,  be  they  muscle,  blood,  nerve,  bone,  or  gristle,  are  built  up 
from  the  nutrients  in  our  food. 

Proteids. — Proteids,  in  some  manner  unknown  to  us,  are  manu- 
factured in  the  bodies  of  green  plants.  Proteid  substances  contain 
the  element  nitrogen.  Hence  such  foods  are  called  nitrogenous 
foods.  Man  must  form  the  protoplasm  of  his  body  (that  is, 
the  muscles,  tendons,  nervous  system,  blood  corpuscles,  the  living 
parts  of  the  bone  and  the  skin,  etc.)  from  nitrogenous  food. 
Some  of  this  he  obtains  by  eating  the  flesh  of  animals,  and  some 
he  obtains  directly  from  plants  (for  example,  peas  and  beans). 
Because  of  their  chemical  composition,  proteids  are  considered  to 

330 


FOODS  AND  DIETARIES  331 

be  flesh-forming  foods.  They  are,  however,  oxidized  to  release 
energy  if  occasion  requires  it. 

Fats  and  Oils.  —  Fats  and  oils,  both  animal  and  vegetable, 
are  the  materials  from  which  the  body  derives  part  of  its  energy. 
The  chemical  formula  of  a  fat  shows  that,  compared  with  other 
food  substances,  there  is  very  little  oxygen  present;  hence  the 
greater  capacity  of  this  substance  for  uniting  with  oxygen.  The 
rapid  burning  ol  fat  compared  with  the  slower  combustion  of  a 
piece  of  meat  or  a  piece  of  bread  illustrates  this.  A  pound  of  butter 
releases  over  twice  as  much  energy  to  the  body  as  does  a  pound  of 
sugar  or  a  pound  of  steak.  Human  fatty  tissue  is  formed  in  part 
from  fat  eaten,  but  carbohydrate  or  even  proteid  food  may  be 
changed  and  stored  in  the  body  as  fat. 

Carbohydrates.  —  We  see  that  the  carbohydrates,  like  the  fats, 
contain  carbon,  hydrogen,  and  oxygen.  Here,  however,  the 
oxygen  and  hydrogen  are  united  in  the  molecule  in  the  same 
proportion  as  are  hydrogen  and  oxygen  in  water.  Carbohydrates 
are  essentially  energy-producing  foods.  They  are,  however,  of  use 
in  building  up  or  repairing  tissue.  It  is  certainly  true  that  in  both 
plants  and  animals,  such  foods  pass  directly,  together  with  foods 
containing  nitrogen,  to  repair  waste  in  tissues,  thus  giving  the 
needed  proportion  of  carbon,  oxygen,  and  hydrogen  to  unite 
with  the  nitrogen  in  forming  the  protoplasm  of  the  body. 

Inorganic  Foods.  —  Water  forms  a  large  part  of  almost  every 
food  substance.  The  human  body,  by  weight,  is  composed  of 
about  60  |)er  cent  water.  It  is  used  to  make  the  blood,  and  a 
sufficient  quantity  is  most  essential  to  health.  When  we  drink 
water,  we  take  with  it  some  of  the  inorganic  salts  used  by  the  body 
in  the  making  of  bone  and  in  the  formation  of  protoplasm.  Sodiiim 
chloride  (table  salt),  an  important  part  of  the  blood,  is  taken  in 
as  a  flavoring  upon  our  meats  and  vegetables.  Phosphate  of 
lime  and  potash  are  important  factors  in  the  formation  of  bone. 

Phosphorus  is  a  necessary  substance  for  the  making  of  living  matter, 
milk,  eggs,  meat,  whole  wheat,  and  dried  peas  and  beans  containing  small 
amounts  of  it.  Iron  also  is  an  extremely  important  mineral,  for  it  is  used 
in  the  building  of  red  blood  cells.  Meats,  eggs,  peas  and  beans,  spinach 
and  prunes,  are  foods  containing  some  iron. 

Some  other  salts,  compounds  of  calcium,  magnesium,  potassium,  and 


332  FOODS  AND  DIETARIES 

phosphorus,  have  been  recently  found  to  aid  the  body  in  many  of  its  most 
important  functions.  The  beating  of  the  heart,  the  contraction  of  muscles, 
and  the  ability  of  the  nerves  to  do  their  work  appear  to  be  due  to  the  pres- 
ence of  minute  quantities  of  these  salts  in  the  body. 

Uses  of  Nutrients.  —  The  following  table  sums  up  the  uses  of 
nutrients  to  man :  ^  — 

Proteid Forms    tissue    (mus- 

White  (albumen)  of  eggs,  curd  cles,  tendon,  and 

(casein)  of  milk,  lean  meat,  probably  fat).  All    serve    as 

gluten  of  wheat,  etc.  fuel    and    yield 

Fats Form  fatty  tissue.  energy   in   form 

Fat  of  meat,  butter,  olive  oil,  of  heat  and  mus- 

oils  of  corn  and  wheat,  etc.  cular  strength. 

Carbohydrates Transformed  into  fat. 

Sugar,  starch,  etc. 
Mineral  matters  (ash) ....     Aid  in  forming  bone, 

Phosphates  of  lime,   potash,  assist  in  digestion,  etc. 

soda,  etc. 

How  the  Exact  Nutritive  Value  of  Food  has  been  Discovered.  —  For 
a  number  of  years,  experiments  have  been  in  progress  in  different  parts 
of  the  civilized  world  which  have  led  to  the  beliefs  regarding  food  just 
quoted.  One  of  the  most  accurate  and  important  series  of  experiments 
was  made  a  few  years  ago  by  the  late  Professor  W.  O.  Atwater  of  Wes- 
leyan  University,  in  cooperation  with  the  United  States  Department  of 
Agriculture.  By  means  of  a  machine  called  the  respiration  calorimeter 
(Latin,  color  =  heat  +  metrum  =  measure),  which  measures  both  the 
products  of  respiration  and  the  heat  given  off  by  the  body,  it  has  been 
possible  to  determine  accurately  the  value  of  different  kinds  6f  food,  both 
as  fuel  and  as  tissue  builders.  This  respiration  calorimeter  is  described 
by  Professor  Atwater  as  follows :  — 

"  Its  main  feature  is  a  copper- walled  chamber  7  feet  long,  4  feet  wide, 
and  6  feet  4  inches  high.  This  is  fitted  with  devices  for  maintaining  and 
measuring  a  ventilating  current  of  air,  for  sampling  and  analyzing  this  air, 
for  removing  and  measuring  the  heat  given  off  within  the  chamber,  and 
for  passing  food  and  other  articles  in  and  out.  It  is  furnished  with  a  fold- 
ing bed,  chair,  and  table,  with  scales  and  appliances  for  muscular  work, 
and  has  telephone  connection  with  the  outside.  Here  the  subject  stays 
for  a  period  of  from  three  to  twelve  days,  during  which  time,  careful 
analyses  and  measurements  are  made  of  all  material  which  enters  the 
body  in  the  food,  and  of  that  which  leaves  it  in  the  breath  and  excreta. 

*  W.  O.  Atwater,  Principles  of  NiUrition  and  Nutritive  Value  of  Food,  U.S.  De- 
partment of  Agriculture,  1902. 


FOODS  AND  DIETARIES  333 

Record  is  also  kept  of  the  energy  given  oflf  from  the  body  as  heat  and 
muscular  work.  The  difference  between  the  material  taken  into  and  that 
given  off  from  the  body  is  called  the  balance  of  matter,  and  shows  whether 
the  body  is  gaining  or  losing  material.  The  difference  between  the  energy 
of  the  food  taken  and  that  of  the  excreta  and  the  energy  given  off  by  the 
body  as  heat  and  muscular  work,  is  the  balance  of  energj%  and,  if  cor- 
rectly measured,  should  equal  the  energy  of  the  body  material  gained  or 
lost.  With  such  apparatus  it  is  possible  to  learn  what  effect  different  con- 
ditions of  nourishment  will  have  on  the  human  body.  In  one  experiment, 
for  instance,  the  subject  might  be  kept  quite  at  rest,  and  in  the  next  do  a 
certain  amount  of  muscular  or  mental  work  with  the  same  diet  as  before, 
then  by  comparing  the  results  of  the  two,  the  use  which  the  body  makes 
of  its  food  under  the  different  conditions  could  be  determined ;  or  the 
diet  may  be  sUghtly  changed  in  the  one  experiment,  and  the  effect  of  this 
on  the  balance  of  matter  or  energy,  observed.  Such  methods  and  appa- 
ratus are  very  costly  in  time  and  money,  but  the  results  are  proportionately 
more  valuable  than  those  from  simpler  experiments." 

Fuel  Values  of  Nutrients.  —  In  experiments  performed  by 
Professor  Atwater  and  others,  and  in  the  appended  tables,  the 
value  of  food  as  a  source  of  energy  is  stated  in  heat  units  called 
calories.  A  calorie  is  the  amount  of  heat  required  to  raise  the  tem- 
perature of  one  kilogram  of  water  from  zero  to  one  degree  Centi- 
grade. This  is  about  equivalent  to  raising  one  pound  four  degrees 
Fahrenheit.  The  fuel  value  of  different  foods  may  be  computed 
in  a  definite  manner.  This  is  done  by  burning  a  given  portion 
of  a  food  (say  one  pound)  in  the  apparatus  known  as  a  calori- 
meter. By  this  means  may  be  determined  the  number  of  degrees 
the  temperature  of  a  given  amount  of  water  is  raised  during  the 
process  of  burning. 

The  Best  Dietary.  —  Inasmuch  as  all  living  substance  contains 
nitrogen,  it  is  evident  that  proteid  food  must  form  a  part  of  the 
dietary ;  but  proteid  alone  is  not  usable.  If  more  proteid  is  eaten 
than  the  body  requires,  then  immediately  the  liver  and  kidneys 
have  to  work  overtime  to  get  rid  of  the  excess  of  proteid  which 
forms  a  poisonous  waste  harmful  to  the  body.  We  must  take  foods 
that  will  give  us,  as  nearly  as  possible,  the  proportion  of  the  dif- 
ferent chemical  elements  as  they  are  contained  in  protoplasm.  It 
has  been  found,  as  a  result  of  studies  of  Atwater  and  others,  that 
a  man  who  does  muscular  work  requires  a  little  less  than  one  quarter 
of  a  pound  of  proteid,  the  same  amount  of  fat,  and  about  one  pound 


334  FOODS  AND  DIETARIES 

of  carbohydrate  to  provide  for  the  growth,  waste,  and  repair  of  the 
body  and  the  energy  used  up  in  one  day.  Put  in  another  way,  At- 
water's  standard  for  a  man  at  light  exercise  is  food  enough  to 
yield  2816  calories;  of  these,  410  calories  are  from  proteid,  930 
calories  from  fat,  and  1476  calories  from  carbohydrate.  That  is, 
for  every  100  calories  furnished  by  the  food,  14  are  from  proteid, 
32  from  fat,  and  54  from  carbohydrate.  In  exact  numbers,  the 
day's  ration  as  advocated  by  Atwater  would  contain  about  100 
grams  or  3.7  ounces  proteid,  100  grams  or  3.7  ounces  fat,  and  360 
grams  or  13  ounces  carbohydrate.  Professor  Chittenden  of  Yale 
University,  another  food  expert,  thinks  we  need  proteids,  fats,  and 
carbohydrates  in  about  the  proportion  of  1  to  3  to  6,  thus  differing 
from  Atwater  in  giving  less  proteid  in  proportion.  Chittenden's 
standard  for  the  same  man  is  food  to  yield  a  total  of  2360  calories, 
of  which  proteid  furnishes  236  calories,  fat  708  calories,  and  car- 
bohydrates 1416  calories.  For  every  100  calories  furnished  by 
the  food,  10  are  from  proteid,  30  from  fat,  60  from  carbohydrate. 
In  actual  amount  the  Chittenden  diet  would  contain  2.16  ounces 
proteid,  2.83  ounces  fat,  and  13  ounces  carbohydrate.^  A  German 
named  Voit  gives  as  ideal  25  proteids,  20  fat,  55  carbohydrate, 
out  of  every  100  calories ;  this  is  nearer  our  actual  daily  ration. 
In  addition,  an  ounce  of  salt  and  nearly  one  hundred  ounces  of 
water  are  used  in  a  day.  By  means  of  the  table  on  the  following 
page  (from  Atwater  ^),  which  shows  the  composition  of  some  food 
materials,  the  nutritive  and  fuel  value  of  the  foods  may  be  seen 
at  a  glance.  The  amount  of  refuse  contained  in  foods  (such  as  the 
bones  of  meat  or  fish,  the  exoskeleton  of  crustaceans  and  mol- 
lusks,  the  woody  coverings  of  plant  cells)  is  also  shown  in  this 
table. 

A  Mixed  Diet  Best.  —  Knowing  the  proportion  of  the  different 
food  substances  required  by  man,  it  will  be  an  easy  matter  to 
determine  from  this  table  the  best  foods  for  use  in  a  mixed  diet. 
Meats  contain  too  much  nitrogen  in  proportion  to  the  other  sub- 
stances. In  milk,  the  proportion  of  proteids,  carbohydrates,  and 
fats  is  nearly  right  to  make  protoplasm ;  a  considerable  amount  of 

*  Page  18,  Bill.  6,  Cornell  Reading  Course. 

2  W.  O.  Atwater,  Principles  of  NiUrition  and  Nviritive  Value  of  Food,  U.S.  De- 
partment of  Agriculture,  1902. 


FOODS  AND  DIETARIES 


335 


5~l,Codfl«h,  dres^f  J 


>s 


f  Beef,  loin 


m% 


Matton,  leg 


Cam,  Bmoked 


,  Codfish,  dreiutcd 


Oysters 


Egg« 


Milk, 
tuv^inuned 


Bntter 


Sngar 


m 


^m^ 


^^^^^-^M 


LLJ 


nz 


mm 


]^a 


w^m 


Table  of  food  values.  Determine  the  percentage  of  water  in  codfish,  loin  of  beef, 
milk,  potatoes.  Percentage  of  refuse  in  leg  of  mutton,  codfish,  eggs,  and 
potatoes.  What  is  the  refuse  in  each  case?  Find  three  foods  containing  a 
high  percentage  of  proteid  ;  of  fat ;  of  carbohydrate.  Find  some  food  in 
which  the  proportions  of  proteid,  fat,  and  carbohydrate  are  combined  in 
the  right  proportions. 


336 


FOODS  AND  DIETARIES 


The  composition  of  a 
bottle  of  milk. 
Why  is  it  con- 
sidered a  good 
food? 


mineral  matter  being  also  present.  For  these  reasons,  milk  is  exten- 
sively used  as  a  food  for  children,  as  it  combines  food  material 
for  the  forming  of  protoplasm  with  mineral  matter  for  the  building 
of  bone.  Some  vegetables  (for  example,  peas 
and  beans)  contain  the  nitrogenous  material 
needed  for  protoplasm  formation  in  consider- 
able proportions,  but  in  a  less  digestible  form 
than  is  found  in  some  other  foods.  Vege- 
tarians, then,  are  correct  in  theory  when 
they  state  that  a  diet  of  vegetables  may 
contain  every- 
thing neces- 
sary to  sustain 
life.  But  a 
mixed  diet  is 
healthier.  A 
purely  vege- 
table diet 
contains  much  waste  material, 
such  as  the  cellulose  forming  the 
walls  of  the  plant  cells,  which 
is    indigestible.      The     Japanese 

army  ration  consists  almost  entirely  of  rice.  A  recent  report  by 
their  surgeon-general  intimates  that  the  diminutive  stature  of 
the  Japanese  may,  in  some   part  at  least,  be  due  to  this  diet. 

The  Relation  of  Work  to  Diet.  —  It  has  been  shown  experimentally 
that  a  man  doing  hard,  muscular  work  needs  more  food  than  a  person 
doing  light  work.  The  mere  exercise  gives  the  individual  a  hearty  ap- 
petite ;  he  eats  more  and  needs  more  of  all  kinds  of  food  than  a  man  or 
boy  doing  light  work.  Especially  is  it  true  that  the  person  of  sedentary 
habits,  who  does  brain  work,  should  be  careful  to  eat  less  food  and  food 
that  will  digest  easily.  His  proteid  food  should  also  be  reduced.  Rich 
.or  hearty  foods  may  be  left  for  the  man  who  is  doing  hard  manual  labor 
out  of  doors,  for  any  extra  work  put  on  the  digestive  organs  takes  away 
just  so  much  the  ability  of  the  brain  to  do  its  work. 

The  Relation  of  Environment  to  Diet.  —  We  are  all  aware  of  the  fact 
that  the  body  seems  to  crave  heartier  food  in  winter  than  in  summer. 
The  temperature  of  the  body  is  maintained  at  98^°  in  winter  as  in  sum- 
mer, but  much  more  heat  is  lost  from  the  body  in  the  cold  weather.  Hence 
feeding  in  winter  should  be  for  the  purpose  of  maintaining  our  fuel  sup- 


Three  portions  of  foods,  each  of  which 
furnishes  about  the  same  amount  of 
nourishment. 


FOODS  AND  DIETARIES  337 

ply.  We  need  heat-producing  food,  and  we  need  more  food  in  winter  than 
in  summer,  the  latter  partly  because  we  exercise  more  in  winter.  We 
may  use  carbohydrates  for  this  purpose,  as  they  are  economical  and 
digestible.  The  inhabitants  of  cold  countries  get  their  heat-releasing 
foods  largely  from  fats,  because  no  plants  are  produced  there.  In 
tropical  countries  and  in  hot  weather  little  proteid  should  be  eaten  and 
a  considerable  amount  of  fresh  fruit  used. 

Food  Economy.  —  The  American  people  are  far  less  economical 
in  their  purcliase  of  food  than  most  other  nations.  Nearly  one 
half  of  the  total  income  of  the  average  workingman  is  spent  on 
food.  Not  only  does  he  spend  a  large  amount  on  food,  but 
he  wastes  money  in  purchasing  the  wrong  kinds  of  food.  A 
comparison  of  the  daily  diets  of  persons  in  various  occupations 
in  this  and  other  countries  show  that  as  a  rule  we  eat  more  than 
is  necessary  to  supply  the  necessary  fuel  and  repair,  and  that  our 
workingmen  eat  more  than  those  of  other  countries.  Another 
waste  of  money  by  the  American  is  in  the  false  notion  that  a  large 
proportion  of  the  daily  dietary  should  be  meat.  Many  people 
think  that  the  most  expensive  cuts  of  meat  are  the  most  nutritious. 
The  falsity  of  this  idea  may  be  seen  by  a  careful  study  of  the  table 
on  page  338,  compiled  by  Atwater,  which  shows  the  relative  amount 
of  various  foods  purchasable  for  10  cents  (present-day  prices  are 
from  20  per  cent  to  50  per  cent  higher  than  here  quoted). 

Daily  Fuel  Needs  of  the  Body.  —  It  has  been  pointed  out  that 
the  daily  diet  should  differ  widely  according  to  age,  occupation, 
time  of  year,  etc.  The  following  table  shows  the  daily  fuel  needs 
for  several  ages  and  occupations:  — 

Daily  Calorie  Needs  (Approximately) 

Obs. 

1.  For  child  under  2  years 900  calories 

2.  For  child  from  2-5  years 1200  calories 

3.  For  child  from  6-9  years 1500  calories 

4.  For  child  from  10-12  years       1800  calories 

5.  For  child  from  12-14  (woman,  light  work  also)    .     .     .  2100  calories 

6.  For  boy  (12-14),  giri  (1.5-16),  man  sedentary  ....  2400  calories 

7.  For  boy  (15-16)  (man,  light  muscular  work)    ....  2700  calories 

8.  For  man,  moderately  active  muscular  work    ....  3000  calories 

9.  For  farmer  (busy  season) 3200  to  4000  calories 

10.  For  ditchers,  excavators,  eto 4000  to  5000  calories 

11.  For  lumbermen,  etc 5000  and  more  calories 

HUNT.  ES.  BIO. — 22 


338 


FOODS  AND  DIETARIES 


CARBOHYDRATES  FUEL  VALUE 


FOOD 
MATERIALS 


Beef,  round 


Beef,  shonlder 


Hntton,  leg 


Pork,  loin 


Pork,  salt,  fat 


Codfish,  fresh, 
dressed 


Oysters  35  cents 
per  qnart 


Milk,  6  cents 
per  qnart 


Eggs,  24  cents 
per  dozen 


Wheat  bread 


Oat  meal 


Beans,  white,  dried 


PoUtoes,  60  cents 
per  bushel 


Sugar 


2>i 


.83 


■ 


.56 


POUNDS  OF  NUTRIENTS  AND  CALORIES  OF  FUEL  VALUE 
IN  10  CENTS  WORTH 


2. 000  OAL. 


4.000  CAL. 


EL 


HZ 


a 


Table  showing  the  cost  of  various  foods.  Using  this  table,  make  up  an  enonomical 
dietary  for  one  day,  three  meals,  for  a  man  doing  moderate  work.  Give 
reasons  for  the  amount  of  food  used  and  for  your  choice  of  foods.  Make 
up  another  dietary  in  the  same  manner,  using  expensive  foods.  What  is 
the  difference  in  your  bill  for  the  day  ? 


FOODS  AND  DIETARIES  339 

This  table  was  worked  out  from  a  knowledge  that  different 
amounts  of  energy  are  released  by  the  body  at  different  times  and 
under  differing  conditions. 

Normal  Heat  Output. —  The  following  table  gives  the  result  of 
some  experiments  made  to  determine  the  hourly  and  daily  expendi- 
ture of  energy  of  the  average  normal  grown  person  when  asleep 
and  awake,  at  work  or  at  rest. 

Average  Normal  Output  op  Heat  from  the  Body 


) 
Conditions  of  Musculab  Activitt 


Man  at  rest,  sleeping 

Man  at  rest,  awake,  sitting  up 

Man  at  light  muscular  exercise  .... 
Man  at  moderately  active  muscular  exercise 
Alan  at  severe  muscular  exercise  .... 
Man  at  very  severe  muscular  exercise      .     . 


AVERAQB 

Caloriks 

PEB  HotJB 


65  calories 
100  calories 
170  calories 
290  calories 
450  calories 
600  calories 


It  is  very  simple  to  use  such  a  table  in  calculating  the  number  of 
calories  which  are  spent  in  twenty-four  hours  under  different  bodily 
conditions.  For  example,  suppose  the  case  of  a  clerk  or  school- 
teacher leading  a  relatively  inactive  Ufe,  who 

sleeps  for  9  hours X    65  calories  =    585 

works  at  desk  9  hours        X  100  calories  =    900 

reads,  writes,  or  studies  4  hours ....     X  100  calories  =    400 
walks  or  does  light  exercise  2  hours     .     .     X  170  calories  =    340 

2225 

This  comes  out,  as  we  see,  very  close  to  example  6  of  the  table  ^ 
on  page  337. 

How  we  may  find  whether  we  are  eating  a  Properly  Balanced 
Diet.  —  We  already  know  approximately  our  daily  calorie  needs 
and  about  the  proportion  of  proteid,  fat,  and  carbohydrate  needed. 
Dr.  Irving  Fisher  of  Yale  University  has  worked  out  a  very  easy 
method  of  determining  whether  one  is  living  on  a  proper  diet.    He 

1  The  above  tables  and  those  which  foUow  have  been  taken  from  the  excellent 
pamphlet  of  the  Cornell  Readmg  Course,  No.  6,  Human  Nutrition, 


340 


FOODS  AND  DIETARIES 


has  made  up  a  number  of  tables,  a  portion  of  which  follow/  in 
which  he  has  designated  portions  of  food,  each  of  which  furnishes 
100  calories  of  energy.  The  tables  show  the  proportion  of  proteid, 
fat,  and  carbohydrate  in  each  food,  so  that  it  is  a  simple  matter 
by  using  such  a  table  to  estimate  the  proportions  of  the  various 
nutrients  in  our  dietary.  We  may  depend  upon  taking  somewhere 
near  the  proper  amount  of  food  if  we  take  a  diet  based  upon  either 
Atwater's,  Chittenden's,  or  Voit's  standard.  One  of  the  most 
interesting  and  useful  pieces  of  home  work  that  you  can  do  is  to 
estimate  your  own  personal  dietary,  using  the  tables  giving  the 
100  calorie  portion  to  see  if  you  have  a  properly  balanced  diet. 
From  the  table  on  page  342  make  out  a  simple  dietary  for  your- 
self, estimating  your  own  needs  in  calories  and  then  picking  out 
100  calorie  portions  of  food  which  will  give  you  the  proper  pro- 
portions of  proteid,  fat,  and  carbohydrate. 

A  Graphic  Method  of  Determining  Food  Values.^  —  Another  method 
to  be  used  in  the  laboratory  or  at  home  is  shown  below.  Suppose  we  take 
any  food  from  our  table,  —  for  example,  milk.  In  the  triangle  at  the  left, 
the  line  PC  represents  the  proteid  value  of  a  given  food,  the  line  CF  repre- 


=  =  =  f 


10    ea    90^    io    jo    60    70 


80     90     100 

A  food  map,   the  composition   of    milk 
being  represented  by  the  point  O. 


80 

N 

\ 

K 

T» 

\ 

\ 

\ 

\ 

\ 

w 



X 

\ 

.^• 

X 

1 

0      X 

«  a 

0   4 

0    j 

«    e 

Y 

0      1 

0     fl 

Kr 

0    90     100 

Food    map  showing  the  normal  rec- 
tangle. 

*  For  more  complete  tables  see  Laboratory  Marvual,  Proh.  XLII.  They  were  com* 
piled  by  Dr.  Irving  Fisher  of  Yale  University,  and  are  reproduced  from  the  Journal 
of  the  American  Medical  Association,  Vol.  XLVIII,  page  16. 

*  See  Irving  Fisher,  "  New  Methods  for  indicating  Food  Values,"  American  Jour- 
nal of  Physiology,  Vol,  XL,  No.  1,  and  "  A  Graphical  Method  in  Practical  Dietetics," 
Journal  of  the  American  Medical  Association,  Vol.  XLIII,  pages  1316-1324. 


FOODS  AND   DIETARIES  341 

senting  its  fat  value ;  F  and  P  represent  100  per  cent  fat  and  proteid 
respectively. 

The  threefold  constitution  of  any  particular  food  may  be  represented 
graphically  by  the  position  of  a  point  0  in  this  triangle.  Thus  the 
point  0  representing  milk  is  located  at  a  height  above  C/^  19  per  cent  of 
the  total  height  of  PC,  which  shows  that  19  per  cent  of  the  food  value 
of  milk  is  proteid;  and  at  a  distance  to  the  right  of  CP  towards  F,  52 
per  cent  of  the  distance,  signifying  that  52  per  cent  of  the  food  value  of 
milk  is  fat. 

In  the  triangle  at  the  right,  the  rectangle  wxyz  is  known  as  the  normal 
rectangle,  and  shows  where  a  well-balanced  food  or  combination  of  foods 
would  be  approximately  located. 

Two  or  more  foods  may  be  plotted  as  follows:  The  combination  of 
portions  equal  in  calorie  value  is  represented  by  a  point  midway  between 
them.  If  the  portions  are  unequal,  the  point  0  will,  of  course,  be  pro- 
portionally nearer  the  point  locating  the  larger  portion.  Likewise,  when 
three  foods  are  combined,  the  point  is  first  located  for  two,  then  this  with 
the  third,  the  resulting  combination  with  the  fourth,  etc. 

Thus  we  can  demonstrate  to  the  eye  the  value  of  various  foods  or 
combinations  of  food  in  a  dietary.  (For  laboratory  directions,  see  Lahora^ 
tory  Manual,  Proh.  XLII.) 

Food  Waste  in  the  Kitchen.  —  Much  loss  occurs  in  the  improper 
cooking  of  foods.  Meats  especially,  when  overdone,  lose  much  of 
their  flavor  and  are  far  less  easily  digested  than  when  they  are 
cooked  rare.  The  chief  reasons  for  cooking  meats  are  that  the 
muscle  fibers  may  be  loosened  and  softened,  and  that  the  bacteria 
or  other  parasites  in  the  meat  may  be  killed  by  the  heat.  The 
common  method  of  frying  makes  foods  less  digestible.  Stewing 
is  an  economical  as  well  as  healthful  method.  A  good  way  to  pre- 
pare meat,  either  for  stew  or  soup,  is  to  place  the  meat,  cut  in  small 
pieces,  in  cold  water,  and  allow  it  to  simmer  for  several  hours. 
Rapid  boiling  toughens  the  muscle  fibers  by  the  too  rapid  coagula- 
tion of  the  albuminous  matter  in  them,  just  as  the  white  of  egg 
becomes  solid  when  heated.  Boiling  and  roasting  are  excellent 
methods  of  cooking  meat.  In  order  to  prevent  the  loss  of  the  nutri- 
ents in  roasting,  it  is  well  to  baste  the  meat  frequently;  thus  a 
crust  is  formed  on  the  outer  surface  of  the  meat,  which  prevents  the 
escape  of  the  juices  from  the  inside. 

Vegetables  are  cooked  in  order  that  the  cells  containing  starch 
grains  may  be  burst  open,  thus  allowing  the  starch  to  be  more  easily 
attacked  by  the  digestive  fluids.     Inasmuch  as  water  may  dissolve 


342 


FOODS  AND  DIETARIES 


Tables  op  Food  Values,  Units 

\   AND   ] 

Prices 

Calories  furnished 

^AMrm  nv  Vr\r\n 

Portion  containing 
100  Food  Units 

Weight 

OF  100 

Calories 

BY 

Price 

PER 

X^AJttXU    yjl     A:\J\JU 

Prot. 

Fat 

Carbo. 

Pound 

1.  Vegetable 

Ounces 

Cents 

Crackers 

2  crackers 

.9 

10 

20 

70 

12 

Wheat  bread 

Thick  slice 

1.3 

9 

7 

84 

5 

Corn  meal 

Cereal  dish 

.96 

10 

5 

85 

4 

Oatmeal 

1^  servings 

5.6 

18 

7 

75 

7.5 

Beans  (baked) 

Side  dish 

2.66 

21 

18 

61 

6 

Rice 

Cereal  dish 

3.1 

10 

1 

89 

10 

Sugar 

3  teaspoons 

.86 

— 

— 

100 

6 

Potatoes  (boiled) 

1  large  size 

33.62 

11 

1 

88 

1.5 

Cabbage 

4  servings 

11 

20 

8 

72 

2.5 

Tomatoes 

4  average  servings 

15.2 

21 

7 

72 

6 

Lettuce 

5  average  servings 

18 

25 

14 

61 

10 

2.  Animal 

Beef  (sirloin) 

Small  steak 

1.4 

31 

69 

— 

30 

Brisket 

Ordinary  serving 

1.80 

42 

58 

— 

8 

Mutton  (leg) 

Large  serving 

1.2 

35 

65 

— 

16 

Pork  (loin) 

Small  serving 

.97 

18 

82 

— 

15 

Ham 

Ordinary  serving 

1.1 

28 

72 

— 

-2 

Veal  (leg) 

Large  serving 

2.4 

73 

27 

— 

18 

Chicken 

Large  serving 

3.2 

79 

21 

— 

24 

Codfish 

2  servings 

4.9 

95 

5 

— 

15 

Oysters 

1  dozen 

6.8 

49 

22 

29 

25 

Lobster 

2  servings 

4.1 

78 

20 

2 

35 

Eggs 

1  large  egg 

2.1 

32 

68 

— 

25 

3.  Dairy  Products 

Whole  milk 

Small  glass 

4.9 

19 

52 

29 

4 

Buttermilk 

U  glass 

9.7 

34 

12 

54 

2 

Butter 

Small  pat 

0.44 

0.5 

99.5 

— 

30 

Cheese  (Amer.) 

li  cubic  inch 

.77 

25 

73 

2 

18 

4.  Fruits,  nuts. 

etc. 

Bananas 

1  large 

3.5 

5 

5 

90 

7 

Oranges 

1  large 

9.4 

6 

3 

91 

7 

Watermelon 

1  whole 

27.0 

6 

6 

88 

3 

Apples 

2 

7.3 

3 

7 

90 

1.5 

Peanuts 

13 

.62 

20 

63 

17 

5 

Chocolate 

i  square 

.56 

8 

72 

20 

40 

FOODS  AND  DIETARIES  343 

out  nutrients  from  vegetable  tissues,  it  is  best  to  boil  them  rapidly 
in  a  small  amount  of  water.  This  gives  less  time  for  the  solvent 
action  to  take  place.  Vegetables  should  be  cooked  with  the  outer 
skin  left  on  when  it  is  possible. 

Problem  XLIII.  A  study  of  some  farms  of  food  ajdulterou- 
tions,     {Laboratory  ManioaZ,  Prob.  XLIII.) 

Adulterations  in  Foods.  —  The  addition  of  some  cheaper  sub- 
stance to  a  food,  with  the  view  to  cheating  the  purchaser,  is  known 
as  adulteration.  Many  foods  which  are  artificially  manufactured 
have  been  adulterated  to  such  an  extent  as  to  be  almost  unfit  for 
food  or  even  harmful.  One  of  the  commonest  adulterations  is  the 
substitution  of  grape  sugar  (glucose)  for  cane  sugar.  Most  cheap 
candy  is  so  made.  Flour  and  other  cereal  foods  are  sometimes 
adulterated  with  some  cheap  substitutes,  as  bran  or  sawdust.  Prob- 
ably the  food  which  suffers  most  from  adulteration  is  milk,  as  water 
can  be  added  without  the  average  person  being  the  wiser.  By 
means  of  an  inexpensive  instrument  known  as  a  lactometeTf  this 
cheat  may  easily  be  detected.  In  most  cities,  the  milk  supply  is 
carefully  safeguarded,  because  of  the  danger  of  spreading  typhoid 
fever  (see  Chapter  XXIX)  from  impure  milk.  Milk  is  often 
treated  with  preservatives  which  kill  the  bacteria  in  it  and  pre- 
vent the  milk  from  souring  rapidly.  Such  preservatives  are  often 
harmful  to  health. 

Coffee,  cocoa,  and  spices  are  subject  to  great  adulteration; 
cottonseed  oil  is  often  substituted  for  olive  oil;  butter  is  too 
frequently  artificial;  while  honey,  sirups  of  various  kinds,  cider 
and  vinegar,  have  all  been  found  to  be  either  artificially  made  from 
cheaper  substitutes  or  to  contain  such  substitutes. 

Pure  Food  Laws.  —  Thanks  to  the  National  Pure  Food  Law 
passed  by  Congress  in  1907,  and  to  the  activity  of  various  city  and 
state  boards  of  health,  the  opportunity  to  pass  adulterated  foods 
on  the  pubhc  is  greatly  lessened. 

Impure  Water.  —  Great  danger  comes  from  drinking  impure 
water.  This  subject  has  already  been  discussed  under  Bacteria, 
where  it  was  seen  that  the  spread  of  typhoid  fever  in  particular  is 
due  to  a  contaminated  water  supply.    As  citizens  we  must  aid  all 


344  FOODS   AND   DIETARIES 

legislation  that  will  safeguard  the  water  used  by  our  towns  and  cities. 
Boiling  water  for  ten  minutes  or  longer  will  render  it  safe  from  all 
organic  impurities. 

Stimulants.  —  We  have  learned  that  food  is  anything  that  sup- 
pHes  building  material  or  releases  energy  in  the  body;  but  some 
materials  used  by  man,  presumably  as  food,  do  not  come  under 
this  head.  Such  are  tea  and  coffee.  When  taken  in  moderate 
quantities,  they  produce  a  temporary  increase  in  the  vital  activities 
of  the  person  taking  them.  This  is  said  to  be  a  stimulation; 
and  material  taken  into  the  digestive  tract,  producing  this,  is  called 
a  stimulant.  In  moderation,  tea  and  coffee  appear  to  be  harmless. 
Some  people,  however,  cannot  use  either  without  ill  effects,  even  in 
small  quantity.  It  is  the  habit  formed  of  relying  upon  the  stimulus 
given  by  tea  or  coffee  that  makes  them  a  danger  to  man.  In  large 
amounts,  they  are  undoubtedly  injurious  because  of  a  stimulant 
called  caffeine  contained  in  them.  Cocoa  and  chocolate,  although 
both  contain  a  stimulant  like  caffeine,  are  in  addition  good  foods, 
having  from  12  per  cent  to  21  per  cent  of  proteid,  from  29  per  cent 
to  48  per  cent  fat,  and  over  30  per  cent  carbohydrate  in  their  compo- 
sition. 

Is  Alcohol  a  Food? — The  question  of  the  use  of  alcohol  has 
been  of  late  years  a  matter  of  absorbing  interest  and  importance 
among  physiologists.  A  few  years  ago  Dr.  Atwater  performed  a 
series  of  very  careful  experiments  by  means  of  the  respiration 
calorimeter,  to  ascertain  whether  alcohol  is  of  use  to  the  body  as 
food.i  In  these  experiments  the  subjects  were  given,  instead  of 
their  daily  allotment  of  carbohydrates  and  fats,  enough  alcohol 
to  supply  the  same  amount  of  energy  that  these  foods  would 
have  given.  The  amount  was  calculated  to  be  about  two  and 
one  half  ounces  per  day,  about  as  much  as  would  be  contained  in 
a  bottle  of  light  wine.^  This  alcohol  was  administered  in  small 
doses  six  times  during  the  day.  Professor  Atwater's  results  may 
be  summed  up  briefly  as  follows :  — 

1  Alcohol  is  made  up  of  carbon,  oxygen,  and  hydrogen.  It  is  very  easily  oxidized, 
but  it  cannot,  as  is  shown  by  the  chemical  formula,  be  of  use  to  the  body  in  tissue 
building,  because  of  its  lack  of  nitrogen. 

2  Alcoholic  beverages  contain  the  follomng  proportions  of  alcohol :  beer,  from 
2  to  5  per  cent ;  wine,  from  10  to  20  per  cent ;  liquors,  from  30  to  70  per  cent.  Pat- 
ent medicines  frequently  contain  as  high  as  60  per  cent  alcohol.     (See  page  350.) 


FOODS  AND   DIETARIES  345 

1.  The  alcohol  administered  was  almost  all  oxidized  in  the  body. 

2.  The  potential  energy  in  the  alcohol  was  transformed  into  heat 
or  muscular  work. 

3.  The  body  did  about  as  well  with  the  rations  including  alcohol 
as  it  did  without  it. 

The  committee  of  fifty  eminent  men  appointed  to  report  on  the 
physiological  aspects  of  the  drink  problem  reported  that  a  large 
number  of  scientific  men  state  that  they  are  in  the  habit  of  taking 
alcoholic  liquor  in  small  quantities,  and  many  report  that  they  do 
not  feel  harm  thereby.  A  number  of  scientists  seem  to  agree 
that  within  limits  alcohol  may  l>e  a  kind  of  food,  although  a  very 
poor  food. 

On  the  other  hand,  we  know  that  although  alcohol  may  techni- 
cally be  considered  as  a  food,  it  is  a  very  unsatisfactory  food  and, 
as  the  following  statements  show,  it  has  an  effect  on  the  nervous 
system  which  foods  do  not  have. 

Alcohol  a  Poison.  —  A  commonly  accepted  definition  of  a  poison 
is  that  it  is  any  substance  which ^  when  taken  into  the  body,  tends  to 
cause  serious  detriment  to  health  or  the  death  of  the  organism.  That 
alcohol  may  do  this  is  well  known  by  scientists.  The  follow- 
ing quotations  show  that  a  large  number  of  very  eminent  pro- 
fessors and  physicians  have  this  belief. 

**  The  rather  recent  experiments  of  At  water,  which  were  made  under 
special  conditions  to  exclude  everything  but  the  one  question  of  the  heat 
and  energj'-producing  action  of  alcohol  in  the  human  body,  have  been 
published  and  quoted  over  and  over  again  as  showing  that  it  is  in  all 
respects  a  valuable  food  and  not  in  any  way  deleterious  to  the  system. 
The  fact  that  these  experiments  had  no  reference  to  the  action  of  the 
agent  on  the  circulatory  or  nervous  systems,  which  are  by  far  its  most 
important  effects,  is  never  mentioned.  The  single  truth  that  alcohol  is 
consumed  in  the  body,  producing  heat  and  energy,  proves  no  more  that 
it  is  a  useful  food,  as  one  of  Professor  Atwater's  colleagues  says,  than 
would  the  fact  that  gunpowder  burns  up,  producing  heat  and  energy, 
prove  it  a  profitable  fuel  for  the  stove."  —  Journal  of  the  American 
Medical  Association,  Editorial,  Nov.  25,  1899,  page  1365. 

*'  Life  is  not  to  be  accounted  for  upon  the  theory  of  oxidation  pro- 
cesses, but  rather  to  be  viewed  under  the  aspect  that  with  the  vital 
processes  is  associated  a  constant  consumption  of  energy  and  transfor- 
mation of  the  same  into  other  forms,  —  work  and  heat.  This  puts  a  new 
aspect  upon  the  theory  that  alcohol  is  a  fuel  food.    Only  substance? 


346  FOODS  AND  DIETARIES 

which  can  enter  the  cell  and  become  living  matter  can  be  food  and  have 
an  animating  effect.    This  alcohol  cannot  do. 

"  Hence  the  idea  that  alcohol  economizes  heat  by  its  abundant  heat 
production  is  a  fallacy."  —  Dr.  A.  Holitscher,  Pirkenhammer,  Interna- 
tional Monatsschrift,  April,  1907. 

"  Obviously  only  such  substances  can  be  called  food  material,  or  be 
employed  for  food,  as,  like  albumen,  fat,  and  sugar,  exert  non-poisonous 
influence  in  the  amounts  in  which  they  reach  the  blood  and  must  circu- 
late in  it  in  order  to  nourish.  .  .  .  Although  alcohol  contributes  energy, 
it  diminishes  working  ability.  We  are  not  able  to  find  that  its  energy  is 
turned  to  account  for  nerve  and  muscle  work.  Very  small  amounts, 
vvhose  food  value  is  insignificant,  show  an  injurious  effect  upon  the 
nervous  system."  —  Professor  Grube,  President  of  the  Royal  Institute  of 
Hygiene,  Munich,  in  the  Miinchener  Neuesten  Nachrichteny  May  19, 
1903. 

*•  In  view  of  the  current  tendency  to  regard  alcohol  as  a  food,  it  seemed 
desirable  to  make  a  study  of  its  effects  on  hepatic  glycogenesis,  for  if 
alcohol  can  replace  the  carbohydrates  in  food,  it  ought  to  spare  the  car- 
bohydrate radical  of  the  tissue  proteids.  An  accumulation  of  glycogen 
in  the  liver  after  exclusive  feeding  with  alcohol  might  therefore  be  ex- 
pected. .  .  . 

**  This  suggestion  was  put  to  an  experimental  test.  The  investigation 
was  carried  out  entirely  on  rabbits  which  were  fed  exclusively  on  alcohol 
for  periods  of  4  to  6  days.  Alcohol  was  given  by  mouth  by  means  of  a 
stomach  tube  in  amounts  varying  between  3  to  9  cc.  per  kilo  per  rabbit, 
diluted  to  30  and  60  per  cent.  As  controls,  rabbits  were  used  that  had 
been  starved  for  the  same  number  of  days  as  the  alcohol  rabbits.  Instead 
of  alcohol,  water  was  given  by  mouth  with  a  stomach  tube.  At  the 
expiration  of  the  periods  named,  the  rabbits  were  killed  under  ether 
anesthesia  and  the  liver  examined  for  glycogen  according  to  Pfliiger's 
shorter  method.  .  .  .  The  results  at  this  stage  of  the  investigation 
showed  that  in  rabbits  fed  exclusively  on  alcohol  (10  cc.  30%  per  kilo,  or 
12  cc.  60  %  per  kilo)  daily  for  four  or  five  days,  there  is  no  accumulation 
of  glycogen  in  the  liver,  which  shows  that  glycogen  is  not  formed  in  the 
liver  of  rabbits  when  fed  on  alcohol  alone."  — William  Salant,  American 
Medicine,  April,  1906,  page  41. 

"Alcohol  is  not  a  Food.  —  It  is  said  to  be  a  food  because  eminent 
chemists  tell  us  it  can  be  oxidized,  but  it  has  been  pointed  out  that  some 
of  the  substances  that  are  most  readily  oxidized  are  the  most  virulent 
poisons.  Alcohol  is  a  poison;  it  acts  as  a  poison;  it  is  oxidized  as  a 
poison.  It  contains  certain  elements  of  food  necessary  for  the  production 
of  heat,  but  they  are  arranged  in  such  a  form  that  they  cannot  be  prop- 
erly utilized  by  our  bodies  as  at  present  constituted.  It  is  not  a  food 
because  it  contains  certain  elements  that  are  necessary  for  the  building 
up  of  our  bodies.    It  is  only  when  these  are  in  proper  form  that  they  do 


FOODS  AND  DIETARIES  U7 

not  in  any  way  act  as  poisonous  susbstances."  —  Professor  G.  Sims  Wood- 
head,  M.A.,  M.D.,  F.R.S.E.,  Professor  of  Pathology,  Cambridge  Univer- 
sity, England. 

"  From  an  exhaustive  definition  we  shall  have  to  class  every  substance 
as  a  poison  which,  on  becoming  mixed  with  the  blood,  causes  a  disturb- 
ance in  the  function  of  any  organ.     That  alcohol  is  such  a  poison  cannot 

be  doubted Very  appropriately  has  the  English  language  named 

the  distiu-bance  caused  by  alcoholic  beverages  intoxication,  which,  by  der- 
ivation, means  poisoning." — Dr.  Adolph  Fick,  Professor  of  Physiology, 
Wiirzburg,  Germany. 

"  We  know  that  alcohol  is  mostly  oxidized  in  our  body.  .  .  .  Aloohol 
is,  therefore,  without  doubt,  a  source  of  living  energy  in  our  body,  but  it 
does  not  follow  from  this  that  it  is  also  a  nutriment.  To  justify  this 
assumption,  proof  must  be  furnished  that  the  living  energy  set  free  by 
its  oxidation  is  utilized  for  the  purpose  of  a  normal  function.  It  is  not 
enough  that  potential  energy  is  transformed  into  living  energy;  the 
transformation  must  take  place  at  the  right  time  and  place,  and  at  defi- 
nite points  in  definite  elements  of  the  tissues.  These  elements  are  not 
adapted  to  be  fed  with  every  sort  of  oxidizable  material.  We  do  not 
know  whether  alcohol  can  furnish  to  the  muscles  and  nerves  a  source  of 
energy  for  the  performance  of  their  functions.  ...  In  general,  alcohol 
has  only  paralyzing  properties,  etc."  —  G.  Bunge,  Lehrhuch  der  Physi- 
ologischen  und  Pathologischen  Chemie. 

*'  Alcohol,  also,  when  not  taken  in  too  large  quantities,  may  be  oxidized 
in  the  body,  and  furnish  a  not  inconsiderable  amount  of  energy.  It  is, 
however,  a  matter  of  controversy  at  present,  whether  alcohol  in  small 
doses  can  be  considered  a  true  foodstuff  capable  of  serWng  as  a  direct 
source  of  energy,  and  of  replacing  a  corresponding  amount  of  fats  and 
carbohydrates  in  the  daily  diet."  —  William  H.  Howell,  American  Text- 
book of  Physiology. 

"  The  nutritive  value  of  alcohol  has  been  the  subject  of  considerable 
discussion  and  not  a  few  experiments.  Some  of  these  tend  to  show  that 
in  moderate  non-poisonous  doses  it  acts  as  a  non-proteid  food  in  dimin- 
ishing the  oxidation  of  proteid,  doubtless  by  becoming  itself  oxidized.  Its 
action,  however,  in  this  respect,  is  relatively  small,  and,  indeed,  a  certain 
proportion  of  the  alcohol  ingested  is  exhaled  with  the  air  of  respiration. 

"  Moreover,  in  large  doses  it  (alcohol)  may  act  in  a  contrary  manner, 
increasing  the  waste  of  tissue  proteid.  It  cannot,  in  fact,  be  doubted  that 
any  small  production  of  energy  resulting  from  its  oxidation  is  more  than 
counterbalanced  by  its  deleterious  influence  as  a  drug  upon  the  tissue  ele- 
ments, and  especially  upon  those  of  the  nervous  system."  —  E.  A.  Schaefer, 
A  Textbook  of  Physiology. 

Dr.  Kellogg  points  out  that  strychnine,  quinine,  and  many  other 
drugs  are  oxidized  in  the  body,  but  surely  cannot  be  called  foods. 


348  FOODS  AND  DIETARIES 

The  following  reasons  for  not  considering  alcohol  a  food  are  taken 
from  his  writings  :  — 

"1.  A  habitual  user  of  alcohol  has  an  intense  craving  for  his  accus- 
tomed dram.  Without  it  he  is  entirely  unfitted  for  business.  One  never 
experiences  such  an  insane  craving  for  bread,  potatoes,  or  any  other 
particular  article  of  food. 

"  2.  By  continuous  use  the  body  acquires  a  tolerance  for  alcohol. 
That  is,  the  amount  which  may  be  imbibed  and  the  amount  required  to 
produce  the  characteristic  effects  first  experienced  gradually  increase 
until  very  great  quantities  are  sometimes  required  to  satisfy  the  craving 
which  its  habitual  use  often  produces.  This  is  never  the  case  with  true 
foods.  .  .  .  Alcohol  behaves  in  this  regard  just  as  does  opium  or  any 
other  drug.     It  has  no  resemblance  to  a  food. 

"  3.  When  alcohol  is  withdrawn  from  a  person  who  has  been  accus- 
tomed to  its  daily  use,  most  distressing  effects  are  experienced.  .  .  . 
Who  ever  saw  a  man's  hand  trembling  or  his  nervous  system  unstrung 
because  he  could  not  get  a  potato  or  a  piece  of  cornbread  for  breakfast? 
In  this  respect,  also,  alcohol  behaves  like  opium,  cocaine,  or  any  other 
enslaving  drug. 

"  4.  Alcohol  lessens  the  appreciation  and  the  value  of  brain  and  nerve 
activity,  while  food  reenforces  nervous  and  mental  energy. 

"  5.  Alcohol  as  a  protoplasmic  poison  lessens  muscular  power,  whereas 
food  increases  energy  and  endurance. 

"  6.  Alcohol  lessens  the  power  to  endure  cold.  This  is  true  to  such  a 
marked  degree  that  its  use  by  persons  accompanying  Arctic  expeditions 
is  absolutely  prohibited.  Food,  on  the  other  hand,  increases  ability  to 
endure  cold.  The  temperature  after  taking  food  is  raised.  After  taking 
alcohol,  the  temperature,  as  shown  by  the  thermometer,  is  lowered. 

"  7.  Alcohol  cannot  be  stored  in  the  body  for  future  use,  whereas  all 
food  substances  can  be  so  stored. 

"  8.  Food  burns  slowly  in  the  body,  as  it  is  required  to  satisfy  the 
body's  needs.  Alcohol  is  readily  oxidized  and  eliminated,  the  same  as 
any  other  oxidizable  drug." 

The  Use  of  Tobacco.  —  A  well-known  authority  defines  a  nar- 
cotic as  a  substance  "  which  directly  induces  sleep,  blunts  the  senses 
and,  in  large  amounts,  produces  complete  insensibility."  Tobacco, 
opium,  chloral,  and  cocaine  are  examples  of  narcotics.  Tobacco 
owes  its  narcotic  influence  to  a  strong  poison  known  as  nicotine. 
Its  use  in  killing  insect  parasites  on  plants  is  well  known.  In  ex- 
periments with  jellyfish  and  other  lowly  organized  animals,  the 
author  has  found  as  small  a  per  cent  as  one  part  of  nicotine  to  one 
hundred  thousand  parts  of  sea  water  to  be  sufficient  to  profoundly 


FOODS  AND  DIETARIES 


349 


affect  an  animal  placed  within  it.  The  illustration  here  given 
shows  its  effect  upon  a  fish,  one  of  the  vertebrate  animals.  Nico- 
tine in  a  pure  form  is 
so  powerful  a  poison 
that  two  or  three 
drops  would  be  suf- 
ficient to  cause  the 
death  of  a  man  by  its 
action  upon  the  nerv- 
ous system,  especially 
the  nerves  controlling; 
the  beating  of  the 
heart.  This  action  is 
well  known  among  boys 
training  for  athletic 
contest.  The  heart  is 
affected;  boys  become 
"short-winded''  as  a 
result  of  the  action  on 
the  heart.  It  has  been 
demonstrated  that  tobacco  has,  too,  an  important  effect  on 
muscular  development.  The  stunted  appearance  of  the  young 
smoker  is  well  known. 


Experiment  (by  Davison)  to  show  how  tobacco  afTects 
the  nervous  system.  The  nicotine,  caught  in  the 
water  by  passing  through  it  the  smoke  from  six 
cigarettes,  was  sufficient  to  kill  the  fish  in  the  jar. 


Brohlem  XL  IV.  A  study  of  some  medical  frauds.  iLabo" 
ratory  Manual,  Prob.  XLIV.) 

Use  and  Abuse  of  Drugs.  —  The  American  people  are  addicted 
to  the  use  of  drugs  and,  especially,  patent  medicines.  A  glance  at 
the  street  car  advertisements  shows  this.  Most  of  the  medicines 
advertised  contain  alcohol  in  greater  quantity  than  beer  or  wine, 
and  nearly  all  of  them  have  opium,  morphine,  or  cocaine  in  their 
composition.  Dr.  George  D.  Haggard  of  Minneapolis  has  shown 
by  many  analyses  that  a  large  number  of  the  so-called  ''  malts," 
"  malt  extracts,"  and  ''  tonics,"  including  several  of  the  best  known 
and  most  advertised  on  the  market,  are  simply  disguised  beers 
and,  frequently,  very  poor  beers  at  that.  These  drugs,  in  addition 
to  being  harmful,  affect  the  person  using  them  in  such  a  manner 


350 


FOODS  AND  DIETARIES 


that  he  soon  feels  the  need  for  the  drug.  Thus  the  drug  habit  is 
formed,  —  a  condition  which  has  wrecked  thousands  of  Uves.  A 
number  of  articles  on  patent  medicines  recently  appeared  in  a 


ff^MflU 


mri 


ml  si  t^  ti)l  tel  KEJ 


The  amounts  of  alcohol  in  some  liquors  and  in  some  patent  medicines. 

a,  beer,  5  %  ;  6,  claret,  8  %  ;  c,  champagne,  9  %  ;  d,  whisky,  50  %  ;  e,  well-known  saraaparilla, 
18  %  ;  /,  g,  h,  much-advertised  nerve  tonics,  20  %,  21  %,  25  %  ;  t,  another  much-advertised 
sarsaparilla  ;  j,  a  well-known  tonic,  28  %  ;  A;,  I,  bitters,  37  %,  44  %  alcohol. 

leading  magazine  and  have  been  collected  and  published  under  the 
title  of  "  The  Great  American  Fraud."  Every  boy  and  girl  should 
read  these  so  as  to  be  forearmed  against  such  evils. 

Reference  Reading  on  Foods 

Sharpe,  A  Laboratory  Manual  for  the  Solution  of  Problems  in  Biology.  American 
Book  Company. 

Davison,  The  Human  Body  and  Health.     American  Book  Company. 

Bulletin  13,  American  School  of  Home  Economics,  Chicago. 

The  Great  American  Fraud.     American  Medical  Association,  Chicago. 

Allen,  Civics  and  Health.     Ginn  and  Company. 

Cornell  University  Reading  Course,  Buls.  6  and  7,  Human  Nutrition. 

Lusk,  Science  and  Nutrition.    W.  B.  Saunders  Company. 

The  Propaganda  for  Reform  in  l^roprietary  Medicines.  American  Medical  Associa- 
tion. 

Some  Government  Publications  on  Nutrition  and  Foods 

(To  be  obtained  from  the  Secretary  of  Agriculture,  Washington.) 
No.   Farmers'  Bulletin  : 
23    Foods  :  Nutritive  Value  and  Cost. 


FOODS   AND  DIETARIES  351 

142  Principles  of  Nutrition  and  Nutritive  Value  of  Food. 

34   Meats :  Composition  and  Cooking. 
128  Eggs :  Their  Use  as  Food. 

85  Fish  as  Food. 
121   Legumes  as  Food. 
132   Nuts  and  their  Use  as  Food. 
298  Corn  and  Corn  Products. 

42   Facts  about  Milk. 
249   Cereal  Breakfast  Foods. 

93   Sugar  as  Food. 
182   Poultry  as  Food. 

295  Potatoes  and  other  Root  Crops  as  Food. 

Reprint  from  Yearbook,  1901,  Atwater,  Dietaries  in  Public  InstittUiona. 
Reprint  from  Yearbook,  1902,  Milner,  Coat  of  Food  related  to  its  Nutritive  Value. 
Experiment  Station,  Circular  46,  Langworthy,  Functions  and  Uses  of  Food. 


XXV.   DIGESTION  AND  ABSORPTION 


Purpose  of  Digestion.  —  We  have  learned  that  starch  and  proteid 
food  of  plants  are  formed  in  the  leaves.  A  plant,  however,  is 
unable  to  make  use  of  the  food  in  this  condition.  Before  it  can 
be  transported  from  one  part  of  the  plant  body  to  another,  it  is 
changed  into  a  soluble  form.  In  this  state  it  can  be  passed  from 
cell  to  cell  by  the  process  of  osmosis.  Much  the  same  condition 
exists  in  animals.    In  order  that  food  may  be  of  use  to  man,  it  must 

be  changed  into  a  state  that 
will  allow  of  its  passage  in  a 
soluble  form  through  the  walls 
of  the  alimentary  canal,  or 
food  tube.  Digestion  consists 
in  the  changing  of  foods  from 
an  insoluble  to  a  soluble  form, 
so  that  they  may  pass  through 
the  walls  of  the  alimentary  canal 
and  become  part  of  the  blood. 

Problem  XLV,  Study  of 
the  digestive  system  of  a  frog 
in  order  better  to  understand 
that  of  man.  {Laboratory 
Manual,  Prob.  XLV.) 

Alimentary  Canal.  —  In  all 

vertebrate  animals,  including 
man,  food  is  normally  taken  in 
the  mouth  and  passed  through 
a  food  tube  during  the  process 
of  digestion.  This  tube  is 
composed  of  different  portions, 
named,  respectively,  as  we 
the  gullet,  stomach,  small  and 


I  J 

Picture  of  the  organs  of  digestion :  a,  in- 
testine, leading  out  of  the  pylorus ;  6,  liver ; 
c,  esophagus ;  d,  pancreas ;  e,  stomach ; 
/,  spleen ;  g,  i,  j,  k,  m,  n,  parts  of  large 
intestine ;  h,  I,  small  intestine.  (From 
Johonnot  and  Bouton.) 

pass  from  the  mouth,  posteriorly, 
large  intestine,  and  rectum. 

352 


DIGESTION  AND  ABSORPTION 


353 


Glands.  —  In  addition  to  the  alimentary  canal  proper,  we  find  a 
number  of  digestive  glands,  varying  in  size  and  position,  connected 
with  the  canal.  As  we  have  already  learned,  a  gland  is  a  col- 
lection of  cells  which  takes  up  materials  from  within  the  body 
and  pours  out  this  material  as  a  secretion.  An  example  of  glands 
in  plants  is  found  in  the  nectar  glands  of  a  flower. 

Certain  substances  called  enzymes  formed  by  glands  cause  the 
digestion  of  food.     The  enzymes  secreted  by  the  cells  of  the  glands 
and  poured  out  into  the  food 
tube     act    upon    insoluble 
foods  so  as  to  change  them 
to  a  soluble  form. 

Structure.  —  The  entire 
inner  surface  of  the  food 
tube  is  covered  with  a  soft 
lining  of  mucous  membrane. 
This  is  always  moist  be- 
cause certain  cells,  called 
mucus  cells,  empty  out 
their  contents  into  the  food 
tube,  thus  lubricating  its 
inner  surface.  When  a 
large  number  of  cells  which 
have  the  power  to  secrete 
fluids  are  collected  together, 
the  surface  of  the  food  tube 
may  become  indented  at 
this  point  to  form  a  pitlike 
gland.  Often  such  depres- 
sions are  branched,  thus 
giving  a  greater  secreting  surface,  as  is  seen  in  the  Figure.  The 
cells  of  the  gland  are  always  supplied  with  blood  vessels  and 
nerves,  for  the  secretions  of  the  glands  are  under  the  control  of 
the  nervous  system.  Think  of  a  sour  pickle  and  note  what 
happens. 

Attached  to  the  digestive  tract  of  man  are  found,  besides  the 
salivary  glands  in  the  mouth,  gastric  glands  in  the  walls  of  the 
stomach,  the  liver  and  the  pancreas,  two  large  glands  which  empty 

HUNT.  E8.  BIO.  23 


Diagram  of  a  gland  :  i,  the  common  tube  which 
carries  off  the  secretions  formed  in  the  cells 
lining  the  cavity  c:  a,  arteries  carrying  blood 
to  the  glands;  v,  veins  taking  blood  away  from 
the  gland. 


354 


DIGESTION  AND   ABSORPTION 


into  the  small  intestine  just  below  the  stomach,  and  certain  glands 
{intestinal  glands)  in  the  wall  of  the  intestine. 

It  will  be  the  purpose  of  this  chapter  to  follow  the  various  food 
substances  in  the  passage  through  the  food  tube  in  order  to  find 
how  and  where  the  changes  take  place  in  the  various  nutrients  which 
prepare  them  to  become  part  of  the  blood. 

Mouth  Cavity  in  Man.  —  In  our  study  of  a  frog  we  found  that 
the  mouth  cavity  had  two  unpaired  and  four  paired  tubes  leading 
from  it.  These  are  (a)  the  gullet  or  food  tube,  (b)  the  windpipe  (in 
the  frog  opening  through  the  glottis),  (c)  the  paired  nostril  holes 
(posterior  nares),  (d)  the  paired  Eustachian  tubes,  leading  to  the 
ear.     All  of  these  openings  are  found  in  man. 


^ 


Opening  of  Eusta- 
chian tube 


Soft  palate  — 


Pharynx 


Epiglottis 

Glottis 
Esophagus 

Laryno) 


Hard  palate 


Tongue 


The  mouth  cavity  of  man. 


In  man  the  mouth  cavity,  and  all  internal  surfaces  of  the  food 
tube,  are  lined  with  a  mucous  membrane.  The  mucus  secreted 
from  gland  cells  in  this  lining  makes  a  slippery  surface  so  that 
the  food  may  slip  down  easily.  The  roof  of  the  mouth  is  formed 
in  front  by  a  plate  of  bone  called  the  hard  palate,  and  a  softer 
continuation  to  the  back  of  the  mouth,  the  soft  palate.  These 
separate  the  nose  cavity  from  that  of  the  mouth  proper.     The  part 


DIGESTION  AND  ABSORPTION 


355 


of  the  space  back  of  the  soft  palate  is  called  the  pharynx,  or  throat 
cavity.  From  the  pharynx  lead  off  the  gullet  and  windpipe,  the 
latter  placed  ventral  to  the  former.  The  lower  part  of  the  buccal 
cavity  is  occupied  by  a  muscular  tongue.  Examination  of  its 
surface  with  a  looking-glass  shows  it  to  be  almost  covered  in  places 
by  tiny  projections  called  papilke.  These  papillae  contain  organs 
known  as  taste  buds,  the  sen- 
sory endings  of  which  deter- 
mine the  taste  of  substances. 
The  tongue  is  also  used  in 
moving  food  about  in  the 
mouth,  and  in  starting  it  on 
its  way  to  the  gullet,  while  it 
plays  an  important  part,  as 
we  know,  in  speaking. 

The  Teeth.  —  In  man  the 
teeth,  unlike  those  of  the  frog, 
are  used  for  the  mechanical 
preparation  of  the  food  for  di- 
gestion. Instead  of  holding 
prey,  they  crush,  grind,  or  tear 
food  so  that  more  surface  may 


Teeth    i,  iucisors;  c,  cauine;  p,  premolars ; 
m,  molars. 


be  given  for  the  action  of  the  digestive  fluids.  The  teeth  of  man 
are  divided,  according  to  their  functions,  into  four  groups.  In  the 
center  of  both  the  upper  and  lower  jaw  in  front  are  found  eight 
teeth  with  chisel-like  edges,  four  in  each  jaw ;  these  are  the  incisors, 
or  cutting  teeth.  Next  is  found  a  single 
tooth  on  each  side  (four  in  all) ;  these  have 
rather  sharp  points;  they  are  the  canines; 
look  for  them  in  a  cat  or  dog.  Then  come 
two  teeth  on  each  side,  eight  in  all,  called 
premolars.  Lastly,  the  flat-top  molars,  or 
grinding  teeth,  of  which  there  are  six  in 
each  jaw.  Food  is  caught  between  irregular 
Section  of  a  tooth :  a,    projections  on  the  surface  of  the  molars  and 

enamel;    b,    dentine;  crushed  tO  a  pulpy  maSS. 
c,  pulp  cavity  contain- 
ing blood  vessels  and  Internal  Structure  of  a  Tooth.  —  If  a  tooth  is 
nerves;  d,  cement.  cut    lengthwise,    it    is    found   to  be  hollow;   this 


356 


DIGESTION  AND  ABSORPTION 


cavity,  called  the  pnlp  cavity,  corresponds  to  the  cavity  containing  marrow 
in  bones.  In  life  it  contains  living  material  —  the  blood  vessels,  nerves, 
and  cells  which  build  up  the  bony  part  of  the  tooth.  The  bulk  of  the 
hard  part  of  the  tooth  consists  of  a  limy  material  called  dentine.  Outside 
of  this  is  a  very  hard  substance  called  enamel;  this  substance,  the  hardest 
in  all  the  body,  is  thickest  on  the  exposed  surface  or  crown  of  the  tooth. 
Each  tooth  is  held  in  its  place  in  the  jawbone  by  a  thin  layer  of  bony 
substance  called  cement. 


Problem  XL  VI.    How  foods  are  chemically  prepared  for  ah- 
sorption  into  the  hlood.     {Laboratory  Manual,  Frob.  XL  VI.) 
id)  In  the  mouth. 
(h)  In  the  stomach. 
(c)  In  the  small  intestine. 


Salivary  Glands.  —  We  are  all  familiar  with  the  substance 
called  saliva  which  acts  as  a  lubricant  in  the  mouth.  SaUva  is 
manufactured  in  the  cells  of  three  pairs  of  glands  which  empty 
into  the  mouth,  and  which  are  called,  according  to  their  position, 

the  parotid  (under  the  ear),  the  suh~ 
maxillary  (under  the  jawbone),  and 
the  sublingual  (under  the  tongue). 
Digestion  of  Starch. — If  we  col- 
lect some  saliva  in  a  test  tube,  add 
to  it  a  httle  starch  paste,  place  the 
tube  containing  the  mixture  for  a 
few  minutes  in  tepid  water,  and  then 
test  with  Fehling's  solution,  we  shall 
find  grape  sugar  present.  Careful 
tests  of  the  starch  paste  and  of  the 
saliva  made  separately  will  usually 
show  no  grape  sugar  in  either. 

If  another  test  be  made  for  grape 
sugar,  in  a  test  tube  containing 
starch  paste,  saliva,  and  a  few  drops 
of  any  weak  acid,  the  starch  will  be  found  not  to  have  changed. 
The  digestion  of  starch  to  grape  sugar  is  caused  by  the  presence  in 
the  saliva  of  an  enzyme,  or  digestive  ferment.  You  will  remember 
that  starch  in  the  growing  corn  grain  was  changed  to  grape  sugar 


A  B 

Experiment  showing  non-osmosis  of 
starch  in  tube  A,  and  osmosis  of 
sugar  in  tube  B. 


DIGESTION  AND  ABSORPTION 


357 


by  an  enzyme  called  diastase.  Here  the  same  action  is  caused 
by  an  enzyme  called  ptyalin.  This  ferment,  as  we  can  prove,  acts 
only  in  an  alkaline  medium  at  about  the  temperature  of  the  lx)dy. 

How  Food  is  Swallowed.  —  After  food  has  been  chewed  and 
mixed  with  saliva,  it  is  rolled  into  little  balls  and  pushed  by  the 
tongue  into  such  position  that  the  muscles  of  the  throat  cavity 
may  seize  it  and  force  it  downward.  Food,  in  order  to  reach  the 
gullet  from  the  mouth  cavity,  must  pass  over  the  glottis,  the  open- 
ing into  the  windpipe,  or  trachea.  When  food  is  in  the  course  of 
being  swallowed,  the  upper  part  of  this  tube  forms  a  trapdoor  over 
the  opening.  When  this  trapdoor  is  not  closed,  and  food  "  goes 
down  the  wrong  way,"  we  choke,  and  the  food  is  expelled  by 
coughing. 

The  Gullet,  or  Esophagus.  —  In  man  this  part  of  the  food  tube 
is  much  longer  proportionately  than  in  the  frog.  Like  the  rest  of 
the  food  tube  it  is  Hned  by  soft  and  moist  mucous  membrane.  The 
wall  is  made  up  of  two  sets  of  muscles,  —  the  inside  ones  running 
around  the  tube ;  the  outer  band  of  muscle  taking  a  longitudinal 
course.  After  food  leaves  the  mouth  cavity,  it  gets  beyond  our 
direct  control,  and  the  muscles  of  the  gullet,  stimulated  to  activity 
by  the  presence  of  food  in  the  tube,  push  the  food  down  to  the 
stomach  by  a  series  of  contractions  until  it  reaches  the  stomach. 
The  gullet  passes  directly  through  a  muscular  partition,  the  dia- 
phragm, which  is  lacking  in  the  frog.  The  diaphragm  separates 
the  heart  and  lungs  from  the 
other  organs  of  the  body  cavity. 

Stomach  of  Man. — The  stomach 
is  a  pear-shaped  organ  capable  of 
holding  about  three  pints.  The 
end  opposite  to  the  gullet,  which 
empties  into  the  small  intestine,  is 
provided  with  a  ring  of  muscle 
forming  a  valve  called  the  pylorus. 

Gastric  Glands. — If  we  open  the 
stomach  of  the  frog,  and  remove 
its  contents  by  carefully  washing, 
its  wall  is  seen  to  be  thrown  into 
folds  internally.   Between  the  folds 


Inside  of  the  stomach  and  intestine, 
showing  the  folds  of  the  mucous 
membrane. 


358 


DIGESTION  AND  ABSORPTION 


in  the  stomach  of  man,  as  well  as  in  the  frog,  are  located  a  number 
of  tiny  pits.  These  form  the  mouths  of  the  gastric  glands,  which 
pour  into  the  stomach  a  secretion  known  as  the  gastric  juice.  The 
gastric  glands  are  little  tubes,  the  lining  of  which  secretes  the  fluid. 
This  fluid  is  largely  water.  It  is  slightly 
acid  in  its  chemical  reaction,  containing  about 
.2  per  cent  free  hydrochloric  acid.  It  also 
contains  a  very  important  enzyme  called 
pepsin,  and  another  less  important  one  called 
rennin. 

Action  of  Gastric  Juice.  —  If  proteid  is 
treated  with  artificial  gastric  juice  at  the 
temperature  of  the  body,  it  will  be  found  to 
become  swollen  and  then  gradually  to  change 
to  a  substance  which  is  soluble  in  water. 

Most  proteid  substances  are  insoluble. 
They  belong  to  the  class  of  substances 
known  as  colloids  —  substances  that  do  not 
easily  pass  through  a  membrane  by  osmosis. 
After  proteid  is  digested  in  the  stomach,  it 
is  known  as  a  peptone.  Digestion  of  proteid 
results  in  a  change  of  a  colloid  substance  to 
one  which  will  diffuse  readily  through  a 
membrane,  or  a  crystalloid.  Peptones  are 
crystalloid  substances. 


A  peptic  gland,  from  the 
stomach,  very  much 
magnified.  A,  central 
or  chief  cell,  which 
make  pepsin ;  B,  bor- 
der cells,  which  make 
acid.  (From  Miller's 
Histology.) 


The  other  enzyme  of  gastric  juice,  called  rennin,  curdles  or  coagulates 
a  proteid  found  in  milk ;  after  the  milk  is  curdled,  the  pepsin  is  able  to 
act  upon  it.  "Junket"  tablets,  which  contain  rennin,  are  used  in  the 
kitchen  to  cause  this  change. 

The  hydrochloric  acid  found  in  the  gastric  juice  acts  upon  lime  and 
some  other  salts  taken  into  the  stomach  with  food,  changing  them  so 
that  they  may  pass  into  the  blood  and  eventually  form  the  mineral  part 
of  bone  or  other  tissue. 

Movement  of  Walls  of  Stomach.  —  The  stomach  walls,  provided  with 
three  layers  of  muscle  which  run  in  an  oblique,  circular,  and  longitudinal 
direction  (taken  from  the  inside  outward),  are  well  fitted  for  the  constant 
churning  of  the  food  in  that  organ.  Here,  as  elsewhere  in  the  digestive 
tract,  the  muscles  are  involuntary,  muscular  action  being  under  the  con- 
trol of  the  so-called  sympathetic  nervous  system.  Food  material  in  the 
stomach  makes  several  complete  circuits  during  the  process  of  digestion 


DIGESTION   AND   ABSORPTION  359 

in  that  organ.  Contrary  to  common  belief,  the  greatest  amount  of  food  is 
digested  after  it  leaves  the  stomach.  But  this  organ  keeps  the  food  in  it 
in  almost  constant  motion  for  a  considerable  time,  a  meal  of  meat  and 
vegetables  remaining  in  the  stomach  for  three  or  four  hours.  While 
movement  is  taking  place,  the  gastric  juice  acts  upon  proteids,  softening 
them,  while  the  constant  churning  movement  tends  to  separate  the  bits 
of  food  into  finer  particles.  Ultimately  the  semifluid  food,  most  of  it  still 
undigested,  is  allowed  to  pass  in  small  amounts  through  the  pyloric  valve, 
into  the  small  intestines.  This  is  done  by  the  expansion  of  the  ringlike 
muscles  of  the  pylorus. 

The  partly  digested  food  in  the  small  intestine  almost  immediately 
comes  in  contact  with  fluids  from  two  glands,  the  liver  and  pancreas.  We 
shall  first  consider  the  function  of  the  pancreas. 

Position  and  Structure  of  the  Pancreas.  —  The  most  imp>or- 
tant  digestive  gland  in  the  human  body  is  the  pancreas.  The 
gland  is  a  rather  diffuse  structure ;  its  duct  empties  in  a  common 
opening  with  the  bile  duct,  a  short  distance  below  the  pylorus. 
In  internal  structure,  the  pancreas  resembles  the  salivary  glands. 


Appearance  of  milk  under  the  nucroscope,  showing  the  natural  grouping  of  the 
fat  globules.  In  the  circle  a  single  group  is  highly  magnified.  Milk  is  one  fonn 
of  an  emulsion.     (S.  M.  Babcock,  Wis.  Bui.  No.  61.) 

Starch  added  to  artificial  pancreatic  fluid  and  kept  at  blood  heat 
is  soon  changed  to  sugar.  Proteid,  under  the  same  conditions,  is 
changed  to  peptone.  Fats,  which  so  far  have  been  unchanged 
except  to  be  melted  by  the  heat  of  the  body,  are  changed  by  the 
action  of  the  pancreas  into  a  form  which  can  pass  through  the 
walls  of  the  food  tube.    If  we  test  pancreatic  fluid,  we  find  it  strongly 


360  DIGESTION  AND  ABSORPTION 

alkaline  in  its  reaction.  If  two  test  tubes,  one  containing  olive  oil 
and  water,  the  other  oHve  oil  and  a  weak  solution  of  caustic  soda, 
an  alkali,  be  shaken  violently  and  then  allowed  to  stand,  the  oil 
and  water  will  quickly  separate,  while  the  oil,  caustic  soda,  and 
water  will  remain  for  some  time  in  a  milky  emulsion.  If  this 
emulsion  be  examined  under  the  microscope,  it  will  be  found  to 
be  made  of  millions  of  little  droplets  of  fat,  floating  in  the  liquid. 
The  presence  of  the  caustic  soda  helped  the  forming  of  the  emul- 
sion. Fat  in  this  form  may  be. absorbed.  Pancreatic  fluid  simi- 
larly emulsifies  fats  and  changes  them  into  soft  soaps  and  fatty 
acids.     The  process  of  this  transformation  is  not  well  understood. 

Liver.  —  The  liver  is  the  largest  gland  in  the  body.  In  man,  it  hangs 
just  below  the  diaphragm,  a  Httle  to  the  right  side  of  the  body.  During  Hfe, 
its  color  is  deep  red.  It  is  divided  into  three  lobes,  between  two  of  which 
is  found  the  gall  bladder,  a  thin-walled  sac  which  holds  the  bile,  a  secretion 
of  the  liver.  Bile  is  a  strongly  alkaline  fluid  of  greenish  color.  It  reaches 
the  intestine  through  a  common  opening  with  the  pancreatic  fluid.  Al- 
most one  quart  of  bile  is  passed  daily  into  the  digestive  canal. 

Functions  of  Bile.  —  The  action  of  bile  on  foods  is  not  very  well 
known.  It  is  slightly  antiseptic,  and  thus  may  prevent  fermenta- 
tion within  the  intestine  by  destroying  bacteria.  It  also  has  the  very 
important  faculty  of  aiding  the  passage  of  fats  through  the  walls  of 
the  intestine.  If  two  funnels,  each  containing  filter  paper,  one 
moistened  with  bile,  the  other  dry,  be  filled  with  oil,  the  oil  will  be 
found  to  pass  through  the  moistened  funnel  with  much  greater  ease. 

Formation  of  Glycogen.  —  Perhaps  the  most  important  func- 
tion of  the  liver  is  the  formation  within  it  of  a  material  called  glyco- 
gen, or  animal  sugar.  The  liver  is  supplied  by  blood  from  two 
sources.  The  greater  amount  of  blood  received  by  the  liver  comes 
directly  from  the  walls  of  the  stomach  and  intestine  to  this  organ. 
It  normally  contains  about  one  fifth  of  all  the  blood  in  the  body. 
This  blood  is  very  rich  in  food  materials,  and  from  it  the  cells  of 
the  liver  take  out  sugars  to  form  glycogen.^  Glycogen  is  stored 
in  the  liver  until  such  a  time  as  a  food  is  needed  that  can  be  quickly 
oxidized ;  then  the  glycogen  is  carried  off  by  the  blood  to  the  tissue 

1  It  is  known  that  glycogen  maybe  formed  in  the  body  from  proteid,  and  possibly 
from  fatty  foods. 


DIGESTION  AND   ABSORPTION 


361 


which  requires  it,  and  there  used  for  this  purpose.  Glycogen  is 
also  stored  in  the  muscles,  where  it  is  oxidized  to  release  energy 
when  the  muscles  are  exercised. 

Brohleni  XL  VII,  A  study  of  where  and  how  digested  foods 
pass  into  tJie  hlood.    {Laboratory  Manual,  Proh.  XL  VII.) 

The  Absorption  of  Digested  Food  into  the  Blood.  —  The  object 
of  digestion  is  to  change  foods  from  an  insoluble  to  a  soluble  form. 
This  has  been  seen  in  the  study  of  the  action  of  the  various  diges- 
tive fluids  in  the  body,  each  of  which  is  seen  to  aid  in  dissolving 
soHd  foods,  changing  them  to  a  fluid,  and,  in  case  of  the  bile,  ac- 
tually assisting  them  to  pass  through  the  wall  of  the  intestine.  A 
small  amount  of  digested  food  may  be  absorbed  by  the  blood  in  the 
blood  vessels  of  the  walls  of  the  stomach.  Most  of  the  absorption, 
however,  takes  place  through  the  walls  of  the  small  intestine. 


Structure  of  the  Small 
Intestine.  —  The  small  intes- 
tine in  man  is  a  slender  tube 
nearly  twenty  feet  in  length 
and  about  one  inch  in  di- 
ameter. Its  walls  contain 
muscles  which,  by  a  series  of 
slow  waves  of  contraction, 
force  the  fluid  food  gradually 
toward  the  posterior  end  of 
the  tube.  The  movements  of 
the  muscles  of  the  coat  are 
of  very  great  importance  in 
the  process  of  absorption,  and 
these  movements  are  caused 
to  a  great  extent  (as  is  the 
secretion  of  the  various  glands 
of  the  food  tube)  by  the  me- 
chanical stimulus  of  the  food 
within  the  food  tube.  If  the 
chief  function  of  the  small 
intestine  is  that  of  absorp- 
tion, we  must  look  for  adap- 
tations which  increase  the 
absorbing  surface  of  the  tube. 
This  is  gained  in  part  by  the 


Diagram  of  a  bit  of  the  wall  of  the  small  intestine, 
greatly  magnified,  a,  mouths  of  intestinal 
glands;  6,  villus  cut  lengthwise  to  show  blood 
vessels  and  lacteal  (in  center)  ;  e,  lacteal  sending 
branches  to  other  villi;  i,  intestinal  glands;  m, 
artery  ;  v,  vein;  I,  t,  muscular  coats  of  intestine 
wall. 


362 


DIGESTION  AND  ABSORPTION 


inner  surface  of  the  tube  being  thrown  into  transverse  folds  which  not 
only  retard  the  rapidity  with  which  food  passes  down  the  intestine,  but 
also  give  more  absorbing  surface.  But  far  more  important  for  absorp- 
tion are  millions  of  little  projections  which  cover  the  inner  surface  of 
the  small  intestine. 

The  Villi.  —  So  numerous  are  these  projections  that  the  whole 
surface  presents  a  velvety  appearance.  Collectively,  these  struc- 
tures are  called  the  villi  (singular  villus).  They  form  the  chief 
organs  of  absorption  in  the  intestine,  several  thousand  being 
distributed  over  every  square  inch  of  surface.  By  means  of  the 
folds  and  villi  the  small  intestine  is  estimated  to  have  an  absorb- 
ing surface  equal  to  twice  that  of  the  surface  of  the  body.  Between 
the  vilU  are  found  the  openings  of  many  small  tubeUke  glands, 
the  intestinal  glands.  These  glands  manufacture  a  digestive  fluid, 
strongly  alkaline,  which  aids  in  diges  ing  fats,  and  acts  some- 
what like  the  pancreatic  fluid. 

Internal  Structure  of  a  Villus.  —  The  internal  structure  of  a  villus 
is  best  seen  in  a  longitudinal  section.  We  find  the  outer  wall  made 
up  of  a  thin  layer  of  cells,  the  epithelial  layer.  It  is  the  duty  of  these 
jugular  vein  ^ells  to  absorb  the  semifluid  food  from  within  the 
intestine.  Underneath  these  cells  lies  a  network 
of  very  tiny  blood  vessels,  while  inside  of  these, 
occupying  the  core  of  the  villus,  are  found  spaces 
which,  because  of  their  white  appearance  after 
absorption  of  fats,  have  been  called  lacteals. 

Absorption  of  Foods.  —  Let  us  now  attempt 
to  find  out  exactly  how  foods  are  passed  from 
the  intestines  into  the  blood.  Food  substances 
in  solution  may  be  soaked  up  as  a  sponge  would 
take  up  water,  or  they  may  pass  by  osmosis  into 
the  cells  lining  the  villus.  These  cells  are 
alive,  and  therefore  have  the  power  of  select- 
ing certain  substances  and  rejecting  others. 
Once  within  the  villus,  the  sugars  and  digested 
proteids  pass  through  tiny  blood  vessels  into 
lagmm  s  o'^i^K  <^w  ^^^q  larger  vessels  comprising  the  portal  circu- 
cuiation.  lation.     These  pass  through  the  liver,  where, 


DIGESTION  AND  ABSORPTION  363 

as  we  have  seen,  sugar  is  taken  from  the  blood  and  stored  as 
glycogen.  From  the  liver,  the  food  within  the  blood  is  sent  to 
the  heart,  from  there  is  pmnped  to  the  lungs,  from  there  returns 
to  the  heart,  and  is  pumped  to  the  tissues  of  the  body.  A  large 
amount  of  water  and  some  salts  are  also  absorbed  through  the 
walls  of  the  stomach  and  intestine  as  the  food  passes  on  its  course. 
The  fats  in  the  form  of  soaps  and  fatty  acids  pass  into  the  space 
in  the  center  of  the  villus.  Later  they  are  changed  into  fats  again, 
probably  in  certain  groups  of  gland  cells  known  as  mesenteric 
glands,  and  eventually  reach  the  blood  by  way  of  the  thoracic 
duct  without  passing  through  the  liver. 

Large  Intestine.  —  The  large  intestine  has  somewhat  the  same  struc- 
ture as  the  small  intestine,  except  that  the  diameter  is  much  greater.  It 
also  contains  no  villi.  Considerable  absorption,  however,  takes  place 
through  its  walls  as  the  mass  of  food  and  refuse  material  is  slowly  pushed 
along  by  the  muscles  within,  its  walls. 

In  this  portion  of  the  intestine  live  millions  of  bacteria,  some  of  which 
manufacture  poisonous  substances  from  the  foods  on  which  they  Uve. 
These  substances  are  easily  absorbed  through  the  walls  of  the  large  in- 
testine, and  passing  into  the  blood,  cause  headaches  or  sometimes  serious 
trouble.  Hence  it  follows  that  the  lower  bowel  should  be  emptied  of  this 
matter  as  frequently  as  possible,  at  least  once  a  day.  Constipation  is 
one  of  the  most  serious  evils  the  American  people  have  to  deal  with,  and 
it  is  largely  brought  about  by  the  artificial  life  which  we  lead,  with  its 
lack  of  exercise,  fresh  air,  and  sleep. 

Vermiform  Appendix.  —  At  the  point  where  the  small  intestine  widens 
to  form  the  large  intestine,  a  baglike  pouch  is  formed.  From  one  side  of 
this  pouch  is  given  off  a  small  tube  about  four  inches  long,  closed  at  the 
lower  end.  This  tube,  the  function  of  which  in  man  is  unknown,  is 
called  the  vermiform  appendix.  It  has  come  to  have  unpleasant  noto- 
riety in  late  years,  as  the  site  of  serious  inflammation.  It  often  becomes 
necessary  to  remove  the  appendix  in  order  to  prevent  this  inflammation 
from  spreading  to  the  surrounding  tissues. 

Hygienic  Habits  of  Eating ;  the  Causes  and  Prevention  of  Dys- 
pepsia. —  From  the  contents  of  the  foregoing  chapter  it  is  evident 
that  the  object  of  the  process  of  digestion  is  to  break  up  solid  food 
so  that  it  may  be  absorbed  to  form  part  of  the  blood.  Any  habits 
we  may  form  of  thoroughly  chewing  our  food  will  evidently  aid 
in  this  process.  Undoubtedly  much  of  the  distress  known  as 
dyspepsia  is  due  to  too  hasty  meals  with  consequent  lack  of  proper 


364 


DIGESTION   AND  ABSORPTION 


mastication  of  food.  The  message  of  Mr.  Fletcher  in  bringing 
before  us  the  need  of  proper  mastication  of  food  and  the  attendant 
evils  of  overeating  is  one  which  we  cannot  afford  to  ignore.  It  is 
a  good  rule  to  go  away  from  the  table  feeling  hungry.  Eating 
too  much  overtaxes  the  digestive  organs  and  prevents  their  working 
to  the  best  advantage.  Still  another  cause  of  dyspepsia  is  eating 
when  in  a  fatigued  condition.  It  is  always  a  good  plan  to  rest  a 
short  time  before  eating,  especially  after  any  hard  manual  work. 
Eating  between  meals  is  also  condemned  by  physicians  because  it 
calls  the  blood  to  the  digestive  organs  at  a  time  when  it  should  be 
in  other  parts  of  the  body. 

Effect  of  Alcohol  on  Digestion.  —  It  is  a  well-known  fact  that 
alcohol  extracts  water  from  tissues  with  which  it  is  in  contact. 
This  fact  works  much  harm  to  the  interior  surface  of  the  food  tube, 
especially  the  walls  of  the  stomach,  which  in  the  case  of  a  hard 
drinker  are  likely  to  become  irritated  and  much  toughened.  In 
small  amounts  alcohol  stimulates  the  secretion  of  the  salivary 
and  gastric  glands,  and  thus  seems  to  aid  in  digestion.  It  is 
doubtful,  however,  whether  this  aid  is  real. 

The  following  results  of  experiments  on  dogs,  published  in  the 
American  Journal  of  Physiology,  Vol.  I,  Professor  Chittenden  of 
Yale  University  gives  as  "  strictly  comparable,"  because  "  they 
were  carried  out  in  succession  on  the  same  day."  They  show 
that  alcohol  retards  rather  than  aids  in  digestion :  — 


Number  of  Experiment 


^a  Lb.  Meat  with  Water 


1*0  Lb.  Meat  with  Dilute 
Alcohol 


XVII   a  9 : 

XVII  $S: 

XVIII  a  8: 

XVIII  i8  2: 

XIX  «9: 
XIX 
XX 
XX 
VI 
VI 


&2: 
a  9: 
j82: 
a  9: 
)3l: 


15  A.M. 
00  P.M. 
30  A.M. 
10  P.M. 
00  A.M. 
30  P.M. 
15  A.M. 

30  P.M. 

15  A.M. 
00  P.M. 


Digested  in  3  hours 
Digested  in  2 :  30  hours 
Digested  in  2 :  30  hours 

Digested  in  2  :  15  hours 
Digested  in  3 :  15  hours 


Digested  in  3  :  15  hours 

Digested  in  3  :  00  hours 

Digested  in  3  :  00  hours 
Digested  in  2  :  45  hours 

Digested  in  3  :  45  hours 


Average 


2 :  42  hours 


3 :  09  hours 


DIGESTION  AND  ABSORPTION  365 

As  a  result  of  his  experiments,  Professor  Chittenden  remarks: 
"  We  believe  that  the  results  obtained  justify  the  conclusion  that 
gastric  digestion  as  a  whole  is  not  materially  modified  by  the 
introduction  of  alcoholic  fluids  with  the  food.  In  other  words, 
the  unquestionable  acceleration  of  gastric  secretion  which  follows 
the  ingestion  of  alcoholic  beverages  is,  as  a  rule,  counterbalanced 
by  the  inhibitory  effect  of  the  alcohohc  fluids  upon  the  chemical 
process  of  gastric  digestion,  with  perhaps  at  times  a  tendency 
towards  preponderance  of  inhibitory  action."  Dr.  Kellogg,  Sir 
WilUam  Roberts,  and  others  have  come  to  the  same  or  stronger 
conclusions  as  to  the  undesirable  action  of  alcohol  on  digestion, 
as  a  result  of  their  own  experiments. 

Horsley  and  Sturge  say:  "  Hundreds  of  men  and  women  who 
haunt  the  out-patient  departments  of  hospitals  suffer  from  chronic 
atony  and  slight  dilatation  of  the  stomach,  which  arise  in  part 
from  the  badly  cooked  food  they  eat,  but  chiefly  owe  their 
origin  to  the  debilitating  effect  of  alcohol  upon  the  muscular 
walls  of  this  organ  and  the  fermentation  of  its  retained  contents." 


XXVI.    THE  BLOOD  AND  ITS  CIRCULATION 

Problem  XL  VIII,  To  study  the  composition  of  the  blood. 
{Laboratory  Manual,  Prob.  XL  VI 1 1.) 

Function  of  the  Blood.  —  The  chief  function  of  the  digestive 
tract  is  to  change  foods  to  such  form  that  they  can  be  absorbed 
through  the  walls  of  the  food  tube  and  become  part  of  the  blood. ^ 
By  means  of  a  system  of  closed  tubes,  this  fluid  tissue  circulates 
to  all  parts  of  the  body,  equalizing  the  body  temperature  by  de- 
positing its  burden  of  food  in  places  where  it  is  most  needed  and 
where  it  will  be  used,  either  in  the  repair  and  building  of  tissues 
or  for  oxidation  within  the  cells  of  the  body  to  release  energy. 

If  we  examine  under  the  microscope  a  drop  of  blood  taken  from 
the  frog  or  man,  we  find  it  made  up  of  a  fluid  called  plasma  and  two 
kinds  of  bodies,  the  so-called  red  corpuscles  and  colorless  corpiiscles, 
floating  in  this  plasma. 

Composition  of  Plasma.  —  The  plasma  of  blood  (when  chemically 
examined  in  man)  is  found,  to  be  largely  (about  90  per  cent)  water. 
It  also  contains  a  considerable  amount  of  proteid,  some  sugar, 
fat,  and  mineral  material.  It  is,  then,  the  medium  which  holds  the 
fluid  food  (or  at  least  part  of  it)  that  has  been  absorbed  from 
within  the  intestine.  The  almost  constant  temperature  of  the 
body  is  also  due,  as  we  shall  see,  to  the  blood  which  brings  to 
the  surface  of  the  body  much  of  the  heat  given  off  by  oxidation  of 
food  in  the  muscles  and  glands  within.  When  the  blood  returns 
from  the  tissues  where  the  food  is  oxidized,  the  plasma  brings  back 
with  it  to  the  lungs  the  carbon  dioxide  Uberated  from  the  tissues  of 
the  body  where  oxidation  has  taken  place.  Blood  returning  from 
the  tissues  of  the  body  has  from  45  to  50  c.c.  of  carbon  dioxide 

*  This  change  is  due  to  the  action  of  certain  enzymes  upon  the  nutrients  in  various 
foods.  But  we  also  find  that  peptones  are  changed  back  again  to  proteids  when 
once  in  the  blood.  This  appears  to  be  due  to  the  reversible  action  of  the  enzymes 
acting  upon  them.     (See  page  72.) 

366 


THE  BLOOD   AND   ITS   CIRCULATION 


367 


to  every  100  c.c.     (See  Chapter  XXVII.)     Some  waste  products, 
to  be  spoken  of  later,  are  also  found  in  the  plasma. 

Clotting  of  Blood.  —  If  fresh  beef  blood  is  allowed  to  stand  overnight, 
it  will  be  found  to  have  separated  into  two  parts,  a  dark  red,  almost  solid 
clot  and  a  thin,  straw-colored  liquid  called  serum.  Serum  is  found  to  be 
made  up  of  about  90  per  cent  water,  8  to  9  per  cent  proteid,  and  from 
1  to  2  per  cent  sugars,  fats,  and  mineral  matter.  In  these  respects  it  very 
closely  resembles  the  fluid  food  that  is  absorbed  from  the  intestines. 

If  another  jar  of  fresh  beef  blood  is  poured  into  a  pan  and  briskly 
whipped  with  a  bundle  of  little  rods  (or  with  an  egg  beater),  a  stringy  sub- 
stance will  be  found  to  stick  to  the  rods.  This,  if  washed  carefully,  is 
seen  to  be  almost  colorless.  Tested  with  nitric  acid  and  ammonia,  it  is 
found  to  contain  a  proteid  substance  called  fibrin. 

Blood  plasma,  then,  is  made  up  of  serum,  a  fluid  portion,  and 
fibrin,  which,  although  in  a  fluid  state  in  the  blood  vessels  within 
the  body,  coagulates  when  blood  is  removed  from  the  blood  vessels. 
It  is  this  coagulation  which  aids  in  the  formation  of  a  blood  clot. 
A  clot  is  simply  a  mass  of  fibrin  threads  with  a  large  number  of 
corpuscles  tangled  within.  The  clotting  of  blood  is  of  great  physi- 
ological importance,  for  otherwise  we  might  bleed  to  death  from  the 
smallest  wound. 

In  blood  within  the  circulatory  system  of  the  body,  the  fibrin 
is  held  in  a  fluid  state  called  fibrinogen.  An  enzyme,  acting  upon 
this  fibrinogen,  the  soluble  proteid 
in  the  blood,  causes  it  to  change 
to  an  insoluble  form,  the  fibrin  of 
the  clot. 

The  Red  Blood  Corpuscle;  its 
Structure  and  Functions.  —  The  red 
corpuscle  in  the  blood  of  the  frog 
is  a  true  cell  of  disklike  form.  The 
red  corpuscle  of  man,  however, 
lacks  a  nucleus.  Its  form  is  that 
of  a  biconcave  disk.  So  small  and 
so  numerous  are  these  corpuscles 
that  over  five  million  are  found  in  a  drop  of  normal  blood. 
The  color,  which  is  found  to  be  a  dirty  yellow  when  separate 
corpuscles  are  viewed  under  the  microscope,  is  due  to  a  proteid 


Human  blood  as  seen  under  the 
high  power  of  the  compound 
microscope  ;  at  the  extreme  light 
is  a  colorless  corpuscle. 


368 


THE   BLOOD   AND  ITS   CIRCULATION 


material  called  hcemoglohin.  Haemoglobin  contains  a  large  amount 
of  iron.  It  has  the  power  of  uniting  very  readily  with  oxygen 
whenever  that  gas  is  abundant,  and,  after  having  absorbed  it,  of 
giving  it  up  to  the  surrounding  media,  when  oxygen  is  there  present 
in  smaller  amounts  than  in  the  corpuscle.  This  function  of  carrying 
oxygen  is  the  one  most  important  function  of  the  red  corpuscle, 
although  the  red  corpuscle  also  removes  part  of  the  carbon  dioxide 
from  the  tissues  on  their  return  to  the  lungs.  The  taking  up  of 
oxygen  is  accompanied  by  a  change  in  color  of  the  mass  of  corpuscles 
from  a  dull  red  to  a  bright  scarlet. 

The  Colorless  Corpuscle ;  Structure  and  Functions.  —  A  colorless 
corpuscle  is  a  cell  irregular  in  outline,  the  shape  of  which  is  con- 
stantly changing.  These  corpuscles 
are  somewhat  larger  than  the  red 
corpuscles,  but  less  numerous,  there 
being  about  one  colorless  corpuscle 
to  every  three  hundred  red  ones. 
They  have  the  power  of  movement, 


mn 


^^re, 


Diagram  showing  how  the  colorless  corpuscles 
pass  through  the  walls  of  the  capillaries 
(smallest  blood  tubes)  and  ingulf  the  bacteria 
at  m. 


A  colorless  corpuscle  catching 
and  eating  a  germ. 


for  they  are  found  not  only  inside  blood  vessels,  but  outside 
the  blood  tubes,  showing  that  they  have  worked  their  way 
between  the  cells  that  form  the  walls  of  the  blood  vessels. 

A  Russian  zoologist,  Metschnikoff,  after  studying  a  number  of 
simple  animals,  such  as  medusae  and  sponges,  found  that  in  such 
animals  some  of  the  cells  lining  the  inside  of  the  food  cavity  take 
up  or  ingulf  minute  bits  of  food.  Later,  this  food  is  changed  into 
the  protoplasm  of  the  cell.     Metschnikoff  beheved  that  the  colorless 


THE  BLOOD  AND  ITS  CIRCULATION  369 

corpuscles  of  the  blood  have  somewhat  the  same  function.  This 
he  later  proved  to  be  true.  Like  the  amoeba,  they  feed  by  ingulfing 
their  prey.  This  fact  has  a  very  important  bearing  on  the  relation 
of  colorless  corpuscles  to  certain  diseases  caused  by  bacteria  within 
the  body.  If,  for  example,  a  cut  becomes  infected  by  bacteria, 
inflammation  may  set  in.  Colorless  corpuscles  at  once  surround 
the  spot  and  attack  the  bacteria.  If  the  bacteria  are  few  in 
number,  they  are  quickly  eaten  by  certain  of  the  colorless  cor- 
puscles, which  are  known  as  phagocytes.  If  bacteria  are  present 
in  great  quantities,  they  may  prevail  and  kill  the  phagocytes  by 
poisoning  them.  The  dead  bodies  of  the  phagocytes  thus  killed 
are  found  in  the  pus,  or  matter,  which  accumulates  in  infected 
wounds.  In  such  an  event,  we  must  come  to  the  aid  of  nature 
by  washing  the  wound  with  some  antiseptic,  as  weak  carbolic 
acid  or  hydrogen  peroxide. 

The  Amount  of  Blood  and  its  Distribution.  —  The  protoplasm  of  the 
body,  as  we  know,  is  composed  largely  of  water.  Blood  forms,  by  weight, 
about  one  thirteenth  of  the  body.  Its  distribution  varies  somewhat  ac- 
cording to  the  position  assumed  by  the  body,  and  the  amount  of  undigested 
food  in  the  stomach  and  intestines.  Normally,  about  one  half  of  the 
blood  of  the  body  is  found  in  or  near  the  organs  lying  in  the  body  cavity, 
about  one  fourth  in  the  muscles,  and  the  rest  in  the  heart,  lungs,  large 
arteries,  and  veins. 

Blood  Temperature.  —  The  temperature  of  blood  in  the  human  body 
is  normally  about  98.5°  Fahrenheit,  although  the  temperature  drops 
almost  two  degrees  after  we  have  gone  to  sleep  at  night.  It  is  highest 
about  5  P.M.  and  lowest  about  4  a.m.  In  fevers,  the  temperature  of  the 
body  sometimes  rises  to  107°  or  higher ;  but  unless  this  temperature  is 
soon  reduced,  death  follows.  Any  considerable  drop  in  temperature  be- 
low the  normal  also  would  mean  death.  Body  heat,  as  we  know,  results 
from  the  oxidation  of  food ;  the  constant  circulation  of  blood  keeping  the 
temperature  nearly  uniform  in  all  parts  of  the  body.  The  body  tempera- 
ture may  be  from  two  to  three  degrees  higher  immediately  after  violent 
exercise.     Why  ? 

Cold-blooded  Animals.  —  In  animals  which  are  called  cold-blooded, 
the  blood  has  no  fixed  temperature,  but  varies  with  the  temperature  of 
the  medium  in  which  the  animal  lives.  Frogs,  in  the  summer,  may  sit 
for  hours  in  water  with  a  temperature  of  almost  100°.  In  winter,  they 
often  endure  freezing  so  that  the  blood  and  lymph  within  the  spaces 
under  the  loose  skin  are  frozen  into  ice  crystals.  Such  frogs,  if  thawed 
out  carefully,  will  live.  This  change  in  body  temperature  is  evidently 
an  adaptation  to  the  mode  of  life. 

HUNT.  ES.  BIO.  —  24 


370 


THE  BLOOD  AND  ITS  CIRCULATION 


Circulation  of  the  Blood  in  Man.  —  The  blood  is  the  carrying 
agent  of  the  body.  Like  a  railroad  or  express  company,  it  takes 
materials  from  one  part  of  the  hmnan  organism  to  another.      This 

it  does  by  means  of  the  organs  of 
circulation  —  the  heart  and  blood 
vessels.  These  blood  vessels  are 
called  arteries  where  they  carry  blood 
away  from  the  heart,  veins  where  they 
bring  blood  back  to  the  heart,  and 
capillaries  where  they  connect  the 
arteries  with  the  veins.  The  organs 
of  circulation  thus  form  a  system  of 
connected  tubes  through  which  the 
blood  flows  in  a  continuous  stream. 

The  Heart;  Position,  Size,  Pro- 
tection.— The  heart  is  a  cone-shaped 
muscular  organ  about  the  size  of  a 
man's  fist.  It  is  located  immediately 
above  the  diaphragm,  and  lies  so  that 
the  muscular  apex,  which  points  down- 
ward, moves  while  beating  against 
the  fifth  and  sixth  ribs,  just  a  little  to 
the  left  of  the  midline  of  the  body. 
This  fact  gives  rise  to  the  notion 
that  the  heart  is  on  the  left  side  of 
the  body.  The  heart  is  surrounded  by  a  loose  membranous  bag 
called  the  pericardium,  the  inner  lining  of  which  secretes  a  fluid  in 
which  the  heart  lies.  When,  for  any  reason,  the  pericardial  fluid 
is  not  secreted,  inflammation  arises  in  that  region.  Do  you  know 
why? 

Internal  Structure  of  Heart. — If  we  should  cut  open  the  heart  of 
a  mammal  down  the  midline,  we  could  divide  it  into  a  right  and  a 
left  side,  each  of  which  would  have  no  internal  connection  with  the 
other.  Each  side  is  made  up  of  a  thin-walled  portion  with  a  rather 
large  internal  cavity,  the  auricle,  which  opens  into  a  smaller  portion 
with  heavy  muscular  walls,  the  ventricle.  The  auricles  occupy  the 
base  of  the  cone-shaped  heart ;  the  ventricles,  the  apex.  Commu- 
nication between  auricles  and  ventricles  is  guarded  by  little  flaps 


Diagram  showing  the  front  half  of 
the  heart  cut  away :  a,  aorta ; 
I,  arteries  to  the  lungs  ;  la,  left 
auricle  ;  Iv,  left  ventricle ;  m, 
tricuspid  valve  open ;  n,  bi- 
cuspid or  mitral  valve  closed; 
p  and  r,  veins  from  the  lungs; 
ra,  right  auricle  ;  rv,  right  ven- 
tricle ;  V,  vena  cava.  Arrows 
show  direction  of  circulation. 


THE  BLOOD  AND  ITS  CIRCULATION 


371 


of  muscle  called  valves.  The  auricles  receive  blood  from  the  veins. 
The  ventricles  pump  the  blood  into  the  arteries.  From  each  ven- 
tricle, large  arteries  leave  the  heart ;  that  of  the  left  side  is  called  the 
aorta.  Through  the  aorta,  blood  passes  to  all  parts  of  the  body. 
From  the  right  ventricle  the  pulmonary  artery  carries  blood  to  the 
lungs.  The  openings  to  these  arteries  are  guarded  by  three  half- 
nioon-shaped  flaps,  which  open  so  as  to  allow  blood  to  pass  away 
from  the  ventricle,  but 
not  to  go  back  into  it 
when  the  muscles  relax. 

The  Heart  in  Action. 
—  The  heart  is  con- 
structed on  the  same 
plan  as  a  force  pump, 
the  .valves  preventing 
the  reflux  of  blood  into 
the  auricle  after  it  is 
forced  out  of  the  ven- 
tricle. Blood  enters 
the  auricles  from  the 
veins  because  the  mus- 
cles of  that  part  of 
the  heart  relax;  this 
allows  the  space  within 
the  auricles  to  fill.  Al- 
most immediately  the  muscles  of  the  ventricles  relax,  thus  allowing 
blood  to  pass  into  the  chambers  within  the  ventricles.  Then, 
after  a  short  pause,  during  which  time  the  muscles  of  the  heart  are 
resting,  a  wave  of  muscular  contraction  begins  in  the  auricles  and 
ends  in  the  ventricles,  with  a  sudden  strong  contraction  which 
forces  the  blood  out  into  the  arteries.  Blood  is  kept  on  its  course 
by  the  valves,  which  act  in  the  same  manner  as  do  the  valves  in  a 
pump,  thus  forcing  the  blood  to  pass  into  the  arteries  upon  the  con- 
traction of  ventricle  walls. 

The  Course  of  the  Blood  in  the  Body.  —  Although  the  two  sides 
of  the  heart  are  separate  and  distinct  from  each  other,  yet  every 
drop  of  blood  that  passes  through  the  left  heart  likewise  passes 
through  the  right  heart.     There  are  two  distinct  systems  of  cir- 


The  heart  is  a  force  pump ;  prove  it  from  these  diagrams. 


372 


THE   BLOOD   AND   ITS   CIRCULATION 


culation  in  the  body.  The  pulmonary  circulation  takes  the  blood 
through  the  right  auricle  and  ventricle,  to  the  lungs,  and  passes  it 
back  to  the  left  auricle.  This  is  a  relatively  short  circulation,  the 
blood  receiving  in  the  lungs  its  supply  of  oxygen,  and  there  giving  up 
some  of  its  carbon  dioxide.  The  greater  circulation  is  known  as 
the  systemic  circulation;  in  this  system,  the  blood  leaves  the  left 
ventricle  through  the  great  dorsal  aorta.  A  large  part  of  the 
blood  passes  directly  to  the  muscles ;  some  of  it  goes  to  the  nervous 
system,  kidneys,  skin,  and  other  organs  of  the  body.  It  gives  up 
its  supply  of  food  and  oxygen  in  these  tissues,  receives  the  waste 


Capillaries 


Diagram  of  the  circulation  of  blood  in 
mammal. 

1  See  Hough  and  Sedgwick, 


products  of  oxidation  while 
passing  through  the  capillaries, 
and  returns  to  the  right  auricle 
through  two  large  vessels  known 
as  the  ven(B  cavce.  It  requires 
from  twenty  to  thirty  seconds 
only  for  the  blood  to  make 
the  complete  circulation  from 
the  ventricle  back  again  to  the 
starting  point.  This  means 
that  the  entire  volume  of  blood 
in  the  human  body  passes  three 
or  four  thousand  times  a  day 
through  the  various  organs  of 
the  body.^ 

Portal  Circulation.  —  Some  of 
the  blood,  on  its  return  to  the 
heart,  passes  by  an  indirect  path 
to  the  walls  of  the  food  tube  and 
to  its  glands.  From  there  it  passes 
with  its  load  of  absorbed  food  to 
the  liver.  Here  the  vein  which 
carries  the  blood  (called  the  portal 
vein)  breaks  up  into  capillaries 
around  the  cells  of  the  liver.  We 
have  already  learned  that  the  liver 
is  a  great  storehouse  of  animal 
sugar  called  glycogen.  This  glyco- 
gen is  a  food  that  may  be  easily 
The  Human  Mechanism,  page  136. 


THE  BLOOD  AND   ITS   CIRCULATION 


373 


oxidized  to  release  energy,  and  is  stored  for  that  purpose.  The  sugar 
that  becomes  glycogen  is  carried  to  the  liver  directly  from  the  walls  of 
the  stomach  and  intestine,  where  it  has  been  absorbed  from  the  food 
there  contained.  From  the  liver,  blood  passes  directly  to  the  right 
auricle.  The  portal  circulation,  as  it  is  called,  is  the  only  part  of  the 
circulation  where  the  blood  passes  through  two  sets  of  capillaries. 

Problem  XLIX.  A  study  of  the  circulation  of  the  blood, 
{ Laboratory  Manual,  Prob.  XLIX,) 

Circulation  in  the  Web  of  a  Frog's  Foot.  —  If  the  web  of  the  foot 
of  a  live  frog  or  the  tail  of  a  tadpole  is  examined  under  the  com- 
pound microscope,  a  network  of  blood  vessels  will  be  seen.  In 
some  of  these  the  corpuscles  are  moving  rapidly  and  in  spurts;  these 
are  arteries.  The  arteries  lead  into  smaller  vessels  hardly  greater 
in  diameter  than  the  width  of  a  single  corpuscle.  This  network  of 
capillaries  may  be  followed  into  larger  veins  in  which  the  blood 
moves  regularly.     This  illustrates  the  condition  in  any  tissue  of 


Capillary  circulation  in  the  web  of  a  frog's  foot,  as  seen  under  the  compound 
microscope,  a,  b,  small  veins ;  c,  pigment  cells  in  the  skin ;  d,  capillaries  in 
which  the  oval  corpuscles  are  seen  to  follow  one  another  in  single  series. 


374 


THE  BLOOD  AND  ITS  CIRCULATION 


man  where  the  arteries"  break  up  into  capillaries,  and  these  in  turn 
form  veins. 

Structure  of  the  Arteries.  —  A  distinct  difference  in  structure 
exists  between  the  arteries  and  the  veins  in  the  human  body.  The 
arteries,  because  of  the  greater  strain  received  from  the  blood  which 
is  pumped  from  the  heart,  have  thicker  muscular  walls,  and  in 
addition  are  very  elastic. 

Cause  of  the  Pulse.  —  The  pulse,  which  can  easily  be  detected  by  press- 
ing the  large  artery  in  the  wrist  or  the  small  one  in  front  of  and  above  the 
external  ear,  is  caused  by  the  gushing  of  blood  through  the  arteries  after 
each  pulsation  of  the  heart.  As  the  large  arteries  pass  away  from  the 
heart,  the  diameter  of  each  individual  artery  becomes  smaller.  At  the 
very  end  of  their  course,  these  arteries  are  so  small  as  to  be  almost 
microscopic  in  size  and  are  very  numerous.  There  are  so  many  that  if 
they  were  placed  together,  side  by  side,  their  united  diameter  would  be 
much  greater  than  the  diameter  of  the  large  artery  (aorta)  which  passes 
blood  from  the  left  side  of  the  heart.  This  fact  is  of  very  great  impor- 
tance, for  the  force  of  the  blood  as  it  gushes  through  the  arteries  becomes 
very  much  less  when  it  reaches  the  smaller  vessels.  This  gushing  move- 
ment is  quite  lost  when  the  capillaries  are  reached,  first,  because  there  is 

so  much  more  space  for  the 
blood  to  fill,  and  secondly, 
because  there  is  considerable 
friction  caused  by  the  very 
tiny  diameter  of  the  capil- 
laries. 

Capillaries.  —  The  cap- 
illaries form  a  network  of 
minute  tubes  everywhere 
in  the  body,  but  especially 
near  the  surface  and  in  the 
lungs.  It  is  through  their 
walls  that  the  food  and 
oxygen  pass  to  the  tissues, 
and  carbon  dioxide  is  given 
up  to  the  plasma.  They 
form  the  connection  that 
completes  the  system  of 
circulation  of  blood  in 
the  body. 


Diagram  of  capillary  circulation.  Note  that 
the  artery  breaks  up  into  smaller  vessels, 
which  unite  again  to  form  a  vein.  The  plasma 
passes  through  the  walls  of  the  capillaries  to 
nourish  the  body  cells ;  some  of  the  lymph 
then  enters  the  lymph  vessels  and  the  rest 
returns  to  the  capillaries. 


THE   BLOOD   AND   ITS   CIRCULATION 


375 


Function  and  Structure  of  the  Veins.  —  If  the  arteries  are  supply- 
pipes  which  convey  fluid  food  to  the  tissues,  then  the  veins  may 
be  hkened  to  drain  pipes  which  carry  away  waste 
material  from  the  tissues.  Extremely  numerous  in 
the  extremities  and  in  the  muscles  and  among  other 
tissues  of  the  body,  they,  Uke  the  branches  of  a  tree, 
become  larger  and  unite  with  each  other  as  they 
approach  the  heart. 

If  the  wall  of  a  vein  is  carefully  examined,  it  will 
be  found  to  be  neither  so  thick  nor  so  tough  as  an 
artery  wall.  When  empty,  a  vein  collapses;  the 
wall  of  an  artery  holds  its  shape.  If  you  hold  your 
hand  downward  for  a  little  time  and  then  examine 
it,  you  will  find  that  the  veins,  which  are  relatively 
much  nearer  the  surface  than  are  the  arteries,  appear 
to  be  very  much  knotted.  This  appearance  is  due 
to  the  presence  of  tiny  valves  within.  These  valves 
open  in  the  direction  of  the  blood  current,  but  would 
close  if  the  direction  of  the  blood  flow  should  be  re- 
versed (as  in  case  a  deep  cut  severed  a  vein).  As 
the  pressure  of  blood  in  the  veins  is  much  less  than 
in  the  arteries,  the  valves  thus  aid  in  keeping  the 
flow  of  blood  in  the  veins  toward  the  heart.  The 
higher  pressure  in  arteries  and  the  suction  in  the  veins  (caused  by 
the  enlargement  of  the  chest  cavity  in  breathing)  are  the  chief 
factors  which  cause  a  steady  flow  of  blood  through  the  veins  in 
the  body. 

Trohlem  L.    Some  changes  in  the  composition  of  the  blood* 

{Laboratory  Manual,  Prdb.  L.) 

Function  of  Lymph.  —  Different  tissues  and  organs  of  the  body 
are  traversed  by  a  network  of  tubes  which  carry  the  blood.  Inside 
these  tubes  is  the  blood  proper,  consisting  of  a  fluid  plasma,  the 
colorless  corpuscles,  and  the  red  corpuscles.  Outside  the  blood 
tubes,  in  spaces  between  the  cells  which  form  tissues,  is  found 
another  fluid,  which  is  in  chemical  composition  very  much  Uke 
plasma  of  the  blood.  This  is  the  lymph.  It  is,  in  fact,  fluid  food 
in  which  some  colorless  amoeboid  corpuscles  are  found.  Blood  gives 


Valves  in  a 
vein.  No- 
tice the  thin 
walls  of  the 
vein. 


376 


THE  BLOOD   AND   ITS   CIRCULATION 


REOy 
CORPUSCLES   „ 


WHITE 
CORPUSCLES 
LEUCOCYTE 


Diagram  showing  the  exchange  between  blood 
and  the  cells  of  the  body. 


up  its  food  material  to  the  lymph.     This  it  does  by  passing  it 
through  the  walls  of  the  capillaries.    The  food  is  in  turn  given  up  to 

the  tissue  cells  which  are 
bathed  by  the  lymph. 

Some  of  the  amoeboid 
corpuscles  from  the  blood 
make  their  way  between 
the  cells  forming  the  walls 
of  the  capillaries.  Lymph, 
then,  is  practically  blood- 
plasma  plus  some  colorless 
corpuscles.  It  acts  as  the 
medium  of  exchange  between 
the  blood  proper  and  the 
cells  in  the  tissues  of  the 
body.  By  means  of  the  food  supply  thus  brought,  the  cells  of  the 
body  are  able  to  grow,  the  fluid  food  being  changed  to  the  proto- 
plasm of  the  cells.  By  means  of  the  oxygen  passed  over  by  the 
lymph,  oxidation  may  take  place  within  the  cells.  Lymph  not 
only  gives  food  to  the  cells  of 
the  body,  but  also  takes  away 
carbon  dioxide  and  other  waste 
materials,  which  are  ultimately 
passed  out  of  the  body  by 
means  of  the  lungs,  skin,  and 
kidneys. 


Lymph  Vessels.  —  The  lymph 
is  collected  from  the  various  tissues 
of  the  body  by  means  of  a  number 
of  very  thin-walled  tubes,  which 
are  at  first  very  tiny,  but  after 
repeated  connection  with  other 
tubes  ultimately  unite  to  form 
large  ducts.  These  lymph  ducts 
are  provided,  like  the  veins,  with 
valves.  The  pressure  of  the  blood 
within  the  blood  vessels  forces 
continually  more  plasma  into  the 
lymph;    thus   a   slow   current   is 


The  lymph  vessels ;  the  dark  spots  are 
lymph  glands:  Zoc,  lacteals;  re,  thoracic 
duct. 


THE  BLOOD   AND   ITS   CIRCULATION  377 

maintained  from  the  lymph  spaces  toward  the  veins.  On  its  course  the 
lymph  passes  through  many  collections  of  gland  cells,  the  lymph  glands. 
In  these  glands  some  impurities  appear  to  be  removed  and  colorless 
corpuscles  made.  The  lymph  ultimately  passes  into  a  large  tube,  the 
tnoracic  ductj  which  flows  upward  near  the  ventral  side  of  the  spinal 
column,  and  empties  into  the  large  subclavian  vein  in  the  left  side 
of  the  neck.  Another  smaller  lymph  duct  enters  the  right  subclavian 
irein. 

The  Lacteals.  —  We  have  already  found  that  part  of  the  digested  food 
(chiefly  carbohydrates,  peptones,  salts,  and  water)  is  absorbed  directly 
into  the  blood  through  the  walls  of  the  villi  and  carried  to  the  liver.  Fat, 
however,  is  passed  into  the  spaces  in  the  central  part  of  the  villi,  and  from 
there  into  other  spaces  between  the  tissues,  known  as  the  lacteals.  The 
lacteals  form  the  most  direct  course  for  the  fats  to  reach  the  blood.  The 
lacteals  and  lymph  vessels  have  in  part  the  same  course.  It  will  be  thus 
seen  that  lymph  at  different  parts  of  its  course  would  have  a  very  differ- 
ent composition. 

The  Nervous  Control  of  the  Heart  and  Blood  Vessels.  —  Although 
the  muscles  of  the  heart  contract  and  relax  without  our  being  able  to  stop 
them  or  force  them  to  go  faster,  yet  in  cases  of  sudden  fright,  or  after  a 
sudden  blow,  the  heart  may  stop  beating  for  a  short  interval.  This  shows 
that  the  heart  is  under  the  control  of  the  nervous  system.  Two  sets  of 
nerve  fibers,  both  of  which  are  connected  with  the  central  nervous  system, 
pass  to  the  heart.  One  set  of  fibers  accelerates,  the  other  slows  or  inhibits, 
the  heartbeat.  The  arteries  and  veins  are  also  under  the  control  of  the 
sympathetic  nervous  system.  This  allows  of  a  change  in  the  diameter 
of  the  blood  vessels.  Thus,  blushing  is  due  to  a  sudden  rush  of  blood  to 
the  surface  of  the  body,  caused  by  an  expansion  of  the  blood  vessels  at 
the  surface.  The  blood  vessels  of  the  body  are  always  full  of  blood.  This 
results  from  an  automatic  regulation  of  the  diameter  of  the  blood  tubes  by 
a  part  of  the  nervous  system  called  the  vasomotor  nerves.  These  nerves 
act  upon  the  muscles  in  the  walls  of  the  blood  vessels.  In  this  way,  each 
vessel  adapts  itself  to  the  amount  of  blood  in  it  at  a  given  time.  After 
a  hearty  meal,  a  large  supply  of  blood  is  needed  in  the  walls  of  the  stomach 
and  intestines.  At  this  time,  the  arteries  going  to  this  region  are  dilated 
so  as  to  receive  an  extra  supply.  "When  the  brain  performs  hard  work, 
blood  is  supplied  in  the  same  manner  to  that  region.  Hence,  one  should 
not  study  or  do  mental  work  immediately  after  a  hearty  meal,  for  blood 
will  be  drawn  away  to  the  brain,  leaving  the  digestive  tract  with  an  in- 
sufficient supply.     Indigestion  may  follow  as  a  result. 

The  Effect  of  Exercise  on  the  Circulation.  —  It  is  a  fact  familiar  to 
all  that  the  heart  beats  more  violently  and  quickly  when  we  are 
doing  hard  work  than  when  we  are  resting.  Count  your  own  pulse 
when  sitting  quietly,  and  then  again  after  some  brisk  exercise  in  the 


378 


THE  BLOOD  AND  ITS  CIRCULATION 


gymnasium.  Exercise  in  moderation  is  of  undoubted  value,  be- 
cause it  sends  the  increased  amount  of  blood  to  such  parts  of  the 
body  where  increased  oxidation  has  been  taking  place  as  the  result 
of  the  exercise.  The  best  forms  of  exercise  are  those  which  give 
as  many  muscles  as  possible  work — walking,  out-of-door  sports,  any 
exercise  that  is  not  violent.  Exercise  should  not  be  attempted  im- 
mediately after  eating,  as  this  causes  a  withdrawal  of  blood  from  the 
walls  of  glands  of  the  digestive  tract  to  the  muscles  of  the  body. 
Neither  should  exercise  be  continued  after  becoming  tired,  as  poisons 
are  then  formed  in  the  muscles,  which  cause  the  feeling  we  call 
fatigue.  Remember  that  extra  work  given  to  the  heart  by  extreme 
exercise  may  injure  it,  causing  possible  trouble  with  the  valves. 

Treatment  of  Cuts  and  Bruises.  —  Blood  which  oozes  slowly 
from  a  cut  will  usually  stop  flowing  by  the  natural  means  of  the 

formation  of  a  clot.  A  cut 
or  bruise  should,  however,  be 
washed  in  a  weak  solution  of 
carbolic  acid  or  some  other 
antiseptic  in  order  to  prevent 
bacteria  from  obtaining  a  foot- 
hold on  the  exposed  flesh.  If 
blood,  issuing  from  a  wound, 
is  bright  red  in  color  and 
gushes  in  distinct  pulsations, 
then  we  know  that  an  artery 
has  been  severed.  To  prevent 
the  flow  of  blood,  a  tight  band- 
age must  be  tied  between  the 
cut  and  the  heart.  A  hand- 
kerchief with  a  knot  placed 
over  the  artery  may  stop  bleed- 
ing if  the  cut  is  on  one  of 
the  limbs.  If  this  does  not 
serve,  then  insert  a  stick  in 
the  handkerchief  and  twist  it 
so  as  to  make  the  pressure  around  the  limb  still  greater.  Thus 
we  may  close  the  artery  until  the  doctor  is  called,  who  may  sew 
up  the  injured  blood  vessel. 


Stopping  flow  of  blood  from  an  artery  by- 
applying  a  tight  bandage  (ligature)  be- 
tween the  cut  and  the  heart. 


THE  BLOOD   AND   ITS  CIRCULATION  379 

The  Effect  of  Alcohol  upon  the  Blood.  —  It  has  recently  been 
discovered  that  alcohol  has  an  extremely  injurious  effect  upon  the 
colorless  corpuscles  of  the  blood,  lowering  their  ability  to  fight  disease 
germs  to  a  marked  degree.  This  is  well  seen  in  a  comparison  of 
deaths  from  certain  infectious  diseases  in  drinkers  and  abstainers, 
the  percentage  of  mortality  being  much  greater  in  the  former. 

Dr.  T.  Alexander  MacNichol,  in  a  recent  address,  said  :  — 

'*  Massart  and  Bordet,  Metchnikoff  and  Sims  Woodhead,  have  proved 
that  alcohol,  even  in  every  dilute  solution,  prevents  the  white  blood  cor- 
puscles from  attacking  invading  germs,  thus  depriving  the  system  of  the 
cooperation  of  these  important  defenders,  and  reducing  the  powers  of 
resisting  disease.  The  experiments  of  Richardson,  Harley,  Kales,  and 
others  have  demonstrated  the  fact  that  one  to  five  per  cent  of  alcohol  in 
the  blood  of  the  living  human  body  in  a  notable  degree  alters  the  appear- 
ance of  the  corpuscular  elements,  reduces  the  oxygen  bearing  elements, 
and  prevents  their  reoxygenation." 

Emphasis  is  frequently  placed  on  the  destruction  and  deterioration  of 
the  leucocytes  or  white  blood  corpuscles  by  writers  on  the  subject.  Dr. 
Grosvener  declares :  — 

*'  The  poisoning  and  paralyzing  influences  of  alcohol  lead  to  the  con- 
clusion that  the  alcoholized  organism  presents  a  lessened  resistance  to  the 
attacks  of  microorganisms.  The  detailed  experiments  of  Abbot  upon 
lower  animals  lean  strongly  toward  the  same  conclusion.  His  experiments 
upon  rabbits  showed  that  the  normal  vital  resistance  to  some  organisms 
was  markedly  diminished.  .  .  . 

"  Rubin  as  reported  in  Journal  oj  Infectious  Diseases,  May  30,  1904, 
studied  the  effect  of  alcohol  upon  infectious  disease  as  shown  in  rabbits. 
He  found  that  the  number  of  leucocytes  was  much  less  in  alcohohzed  than 
in  the  control  rabbits,  that  as  soon  as  the  leucocytes  began  to  decrease  the 
bacteria  increased,  that  there  existed  a  negative  chemotoxis." 

Alcohol  in  the  stomach  is  rapidly  absorbed  and  passes  into  the  blood 
stream.  There  the  strong  affinity  of  alcohol  for  oxygen,  which  leads 
them  to  enter  very  rapidly  into  chemical  combination,  causes  the  alcohol 
to  appropriate  the  oxygen  of  the  red  corpuscles  of  the  blood,  which,  as 
we  have  seen,  are  the  great  oxygen  carriers  in  the  body.  This  tends  to 
impoverish  the  blood  and  render  it  less  valuable  to  the  tissues.  —  Macy, 
Physiology. 

The  Effect  of  Alcohol  on  the  Circulation.  —  Alcoholic  drinks 
affect  the  very  delicate  adjustment  of  the  nervous  centers  control- 
ling the  blood  vessels  and  heart.  Even  very  dilute  alcohol  acts 
upon  the  muscles  of  the  tiny  blood  vessels,  consequently,  more 


380  THE  BLOOD  AND  ITS  CIRCULATION 

blood  is  allowed  to  enter  them,  and,  as  the  small  vessels  are  usually 
near  the  surface  of  the  body,  the  habitual  redness  seen  in  the  face 
of  hard  drinkers  is  the  ultimate  result. 

As  a  result  of  experiments  performed  in  1869,  Zimmerberg  declares : 
"  In  the  light  of  these  experiments  one  is  not  only  justified  in  denying  to 
alcohol  any  stimulating  power  whatever  for  the  heart,  but,  on  the  con- 
trary, in  declaring  that  it  lowers  the  working  capacity  of  that  organ." 

Dr.  J.  H.  Kellogg,  head  of  the  Battle  Creek  Sanitarium,  says :  "  The 
full  bounding  pulse  usually  produced  by  the  administration  of  an  ounce 
or  two  of  brandy  properly  diluted,  gives  the  impression  of  an  increased 
vigor  of  heart  action;  but  it  is  only  necessary  to  determine  the  blood 
pressure  by  means  of  a  Riva-Rocci  instrument,  or  Gaertner's  tonometer, 
to  discover  that  the  blood  pressure  is  lowered  instead  of  raised.  This 
lowering  may  amount  to  twenty  or  thirty  millimeters,  or  even  more.  .  .  . 
It  can  readily  be  seen,  then,  that  the  bounding  pulse  is  not  the  result  of 
increased  heart  vigor,  but  indicates  rather  a  weakened  state  of  the  heart, 
combined  with  a  dilated  condition  of  the  small  vessels." 

In  an  address  before  the  Liverpool  Medical  Association,  Dr.  James 
Barr,  president  of  the  association,  discussing  the  effects  of  medicinal  doses 
of  alcohol  upon  the  circulation,  remarked :  "It  causes  dilatation  of  the 
arterioles  and  of  all  arteries  well  supplied  with  muscular  fibers,  owing  to 
its  paretic  effect  upon  the  vasomotor  nervous  system,  and  its  direct  action 
as  a  protoplasmic  poison  on  the  muscular  fiber.  It  has  a  similar,  though 
less  marked,  action  on  the  cardiac  muscle.  From  these  causes  the  systolic 
blood  pressure  is  lowered,  the  systolic  output  from  the  heart  is  diminished, 
and  the  cardiac  energy  is  wasted  in  pumping  blood  into  relaxed  vessels ; 
the  large  bounding  pulse  with  comparatively  short  systolic  period,  which 
gives  a  deceptive  appearance  of  vigor  and  force  in  the  circulation,  is  due 
to  the  large  wave  in  the  dilated  vessels." 

"  The  first  effect  of  diluted  alcohol  is  to  make  the  heart  beat  faster. 
This  fiUs  the  smaU  vessels  near  the  surface.  A  feeling  of  warmth  is  pro- 
duced which  causes  the  drinker  to  feel  that  he  was  warmed  by  the  drink. 
This  feeling,  however,  soon  passes  away,  and  is  succeeded  by  one  of  chilli- 
ness. The  body  temperature,  at  fiirst  raised  by  the  rather  rapid  oxida- 
tion of  the  alcohol,  is  soon  lowered  by  the  increased  radiation  from  the 
surface. 

"  The  immediate  stimulation  to  the  heart's  action  soon  passes  away 
and,  like  other  muscles,  the  muscles  of  the  heart  lose  power  and  contract 
with  less  force  after  having  been  excited  by  alcohol."  —  Macy,  Physiology. 

Alcohol,  when  brought  to  act  directly  on  heart  muscle,  lessens  the  force 
of  the  beat.  It  may  even  cause  changes  in  the  tissues,  which  eventually 
result  in  the  breaking  of  the  walls  of  a  blood  vessel  or  the  plugging  of  a 
vessel  with  a  blood  clot.  This  condition  may  cause  the  disease  known  as 
apoplexy. 


THE  BLOOD  AND  ITS  CIRCULATION  381 

Effects  of  Tobacco  upon  the  Circulation.  — "  The  frequent  use  of 
cigars  or  cigarettes  by  the  young  seriously  afifects  the  quality  of  the  blood. 
The  red  blood  corpuscles  are  not  fully  developed  and  charged  with  their 
normal  supply  of  life-giving  oxygen.  This  causes  paleness  of  the  skin, 
often  noticed  in  the  face  of  the  young  smoker.  Palpitation  of  the  heart 
is  also  a  common  result,  followed  by  permanent  weakness,  so  that  the 
whole  system  is  enfeebled,  and  mental  vigor  is  impaired  as  well  as  phys- 
ical strength."  —  Macy,   Physiology. 


XXVII.  RESPIRATION  AND   EXCRETION 


Trohlem  LI,    A  study  of  the  organs  and  process  of  respiror 
tion.    {Laboratory  Manual,  Proh.  LI.) 
ia)  Organs  of  respiration  in  frog, 
(b)  Mechanics  of  respiration, 
(o)  Process  of  respiration  in  the  lungs. 

Necessity  for  Respiration.  —  We  have  seen  that  plants  and  ani- 
mals need  oxygen  in  order  that  the  life  processes  may  go  on.  Food 
is  oxidized  to  release  energy,  just  as  coal  is  burned  to  give  heat 
to  run  an  engine.  As  a  draft  of  air  is  required  to  make  fire  under 
the  boiler,  so,  in  the  human  body,  oxygen  must  be  given  so  that 
foods  or  tissues  may  be  oxidized  to  release  energy  used  in  growth. 
This  oxidation  takes  place  in  the  cells  of  the  body,  be  they  part  of  a 
muscle,  a  gland,  or  the  brain.     Blood,  in  its  circulation  to  all  parts 

of  the  body,  is  the  medium 
which  conveys  the  oxygen  to 
that  place  in  the  body  where 
it  will  be  used. 

The  Organs  of  Respira- 
tion in  Man.  —  We  have 
alluded  to  the  fact  that 
the  lungs  are  the  organs 
which  give  oxygen  to  the 
blood  and  take  from  it 
carbon  dioxide.  The 
course  of  air  passing  from 
the  outside  of  the  lungs  in 
man  is  much  the  same  as 
the   frog.     Air 


f—l 


in 


Air  passages  in  the  human  lungs:  a,  larynx ;  6, 
trachea  (or  windpipe) ;  c,  d,  bronchi ;  e,  bron- 
chial tubes ;  /,  cluster  of  air  cells.  , .  ,        , ,  ,  i 

through  the  nares,  the 
glottis,  and  into  the  windpipe.  This  cartilaginous  tube,  the  top 
of  which  may  easily  be  felt  as  the  Adam's  apple  of  the  throat, 

382 


RESPIRATION  AND   EXCRETION 


383 


divides  into  two  bronchi.  The  bronchi  within  the  lungs  break  up 
into  a  great  number  of  smaller  tubes,  the  bronchial  tubes,  which 
divide  somewhat  like  the  small  branches  of  a  tree.  This  branch- 
ing increases  the  surface  of  the  air  tubes  within  the  lungs.  The 
bronchial  tubes,  indeed  all  the  JBroncKial 

passages,    are   lined   with  TijlDe 

I 


Ftowv 
■pulmoriaTy 

artery 


•pvcL-monarv 
uevn 


Diagram  to  show  what  the  blood  loses  and 
gains  in  one  of  the  air  sacs  of  the  lungs. 


air 

ciUated  cells.  The  ciha  of 
these  cells  are  constantly  in 
motion,  beating  with  a  quick 
stroke  toward  the  outer  end 
of  the  tube,  that  is,  toward 
the  mouth.  Hence,  if  any- 
foreign  material  should  get 
into  the  windpipe  or  bronchial 
tubes,  it  will  be  expelled  by 
the  action  of  the  cilia.  It  is 
by  means  of  cilia  that  phlegm 
is  raised  from  the  throat. 
Such  action  is  of  great  im- 
portance, as  it  prevents  the 
filling  of  the  air  passages  with 
foreign  matter.  The  bronchi 
end  in  very  minute  air  sacs  called  alveoli,  —  little  pouches  having 
elastic  walls, —  into  which  air  is  taken  when  we  inspire  or  take  a 
deep  breath.  In  the  walls  of  the  alveoli  are  numerous  capil- 
laries, the  ends  of  arteries  which  pass  from  the  heart  into  the 
lung.  It  is  through  the  very  thin  walls  of  the  alveoli  that  an  inter- 
change of  gases  takes  place  which  results  in  the  blood  giving  up  part 
of  its  load  of  carbon  dioxide^  and  taking  up  oxygen  in  its  place. 

The  Pleura.  —  The  lungs  are  covered  with  a  thin  elastic  membrane, 
the  pleura.  This  forms  a  bag  in  which  the  lungs  are  hung.  Between  the 
walls  of  the  bag  and  the  lungs  is  a  space  filled  with  lymph.  By  this  means 
the  lungs  are  prevented  from  rubbing  against  the  walls  of  the  chest. 

Breathing.  —  In  every  full  breath  there  are  two  distinct  movements, 
inspiration  (taking  air  in)  and  expiration  (forcing  air  out).  In  man  an 
inspiration  is  produced  by  the  contraction  of  the  muscles  between  the 
ribs  together  with  the  contraction  of  the  diaphragm,  the  muscular  wall 
just  below  the  heart  and  lungs ;  this  results  in  pulUng  down  the  diaphragm 
and  pulling  upward  and  outward  of  the  ribs,  thus  making  the  space  within 


384 


RESPIRATION   AND   EXCRETION 


diaphragm^ 


Diagram  showing  portion  of  diaphragm  and  ribs 
in  (a)  inspiration  ;  (6)  expiration. 


the  chest  cavity  larger.     The  lungs,  which  lie  within  this  cavity,  are  filled 
by  the  air  rushing  into  the  larger  space  thus  made.     An  expiration  is 

simpler  than  an  inspiration, 
for  it  requires  no  muscular 
effort ;  the  muscles  relax, 
the  breastbone  and  ribs  sink 
into  place,  while  the  dia- 
phragm returns  to  its  orig- 
inal position. 

A  piece  of  apparatus 
which  illustrates  to  a  de- 
gree the  mechanics  of 
breathing  may  be  made  as 
follows  :  Attach  a  string  to 
the  middle  of  a  piece  of 
sheet  rubber.  Tie  the  rub- 
ber over  the  large  end  of  a 
bell  jar.  Pass  a  glass  Y 
tube  through  a  rubber  stop- 
per. Fasten  two  small  toy 
balloons  to  the  branches  of  the  tube.  Close  the  small  end  of  the  jar  with 
the  stopper.  Adjust  the  tube  so  that  the  balloons  shall  hang  free  in  the 
jar.  If  now  the  rubber  sheet  is  pulled  down  by  means  of  the  string,  the 
air  pressure  in  the  jar  is  reduced  and  the  toy  balloons  within  expand, 
owing  to  the  air  pressure  down  the  tube.  When  the 
rubber  is  allowed  to  go  back  to  its  former  position, 
the  balloons  collapse. 

Rate  of  Breathing  and  Amount  of  Air  Breathed. 
—  During  quiet  breathing,  the  rate  of  inspiration  is 
from  fifteen  to  eighteen  times  per  minute  ;  this  rate 
largely  depends  on  the  amount  of  physical  work  per- 
formed. About  30  cubic  inches  of  air  are  taken  in 
and  expelled  during  the  ordinary  quiet  respiration. 
The  air  so  breathed  is  called  tidal  air.  In  a  "  long 
breath,"  we  take  in  about  100  cubic  inches  in  ad- 
dition to  the  tidal  air.  This  is  called  complemental 
air.  By  means  of  a  forced  expiration,  it  is  possible 
to  expel  from  75  to  100  cubic  inches  more  than  tidal 
air ;  this  air  is  called  reserve  air.  What  remains  in 
the  lungs,  amounting  to  about  100  cubic  inches,  is 
called  the  residual  air.  The  value  of  deep  breathing 
is  seen  by  a  glance  at  the  diagram.  It  is  only  by  this  means  that  we  clear 
the  lungs  of  the  reserve  air  with  its  accompanying  load  of  carbon  dioxide. 
Respiration  under  Nervous  Control.  —  The  muscular  movements 
which  cause  an  inspiration  are  partly  under  the  control  of  the  wiU,  but  in 


Apparatus  showing 
mechanics  of  breath- 
ing. 


RESPIRATION   AND   EXCRETION 


385 


230 
cu.  in. 


part  the  movement  is  beyond  our  control. 
The  nerve  centers  which  govern  inspiration 
are  part  of  the  sympathetic  nervous  system. 
Anything  of  an  irritating  nature  in  the  trachea 
or  larynx  will  cause  a  sudden  expiration  or 
cough.  When  a  boy  runs,  the  quickened  res- 
piration is  due  to  the  fact  that  oxygen  is  used 
up  rapidly  and  a  larger  quantity  of  carbon  di- 
oxide is  formed.  Thus  the  nervous  center 
which  has  control  of  respiration  is  stimulated 
to  greater  activity,  and  quickened  inspiration 
follows. 

I*roblein  LIT.  A  study  of  the  prod- 
ucts of  respiration.  {Laboratory  Man- 
ual,  Prob.  LI  I.) 

Changes  in  Air  in  the  Lungs.  —  Air  is 
much  wanner  after  leaving  the  lungs 
than  before  it  enters  them.  Breathe  on 
the  bulb  of  a  thermometer  to  prove  this. 
Expired  air  contains  a  considerable 
amount  of  moisture,  as  may  be  proved 
by  breathing  on  a  cold  polished  surface. 
This  it  has  taken  up  in  the  air  sacs  of 
the  lungs.  The  presence  of  carbon  di- 
oxide in  expired  air  may  easily  be  de- 
tected by  the  limewater  test.  Air  such  as  we  breathe  out  of  doors 
contains,  by  volume :  — 

Nitrogen 79 

Oxygen 20.96 

Carbon  dioxide .04 


' 

Ciilii ph  II 
\  i  1 

,r„t 

al 

I'KI  tv/. 

in. 

Tidal 

Ail- 

.:n  ci(. 

in. 

Ju  SI  ll\ 

^;M 

/on  ril 

ni . 

i:.sni 

ml 

Ail 

loo  cn 

1)1. 

^ 

Diagram  showing  the  relative 
amounts  of  tidal,  comple- 
mental,  reserve,  and  resid- 
ual air.  The  brace  shows 
the  average  lung  capacity 
for  the  adult  man. 


Air  expired  from  the  lungs  contains :  — 

Nitrogen 70 

Oxygen 16.02 

Carbon  dioxide 4.38 

Water        60 

In  other  words,  there  is  a  loss  of  between  four  and  five  per  cent 
oxygen,  and  nearly  a  corresponding  gain  in  carbon  dioxide,  in 
expired  air.     There  are  also  some  other  organic  substances  present. 

HUNT.   ES.   BIO.  —  25 


386 


RESPIRATION  AND  EXCRETION 


The  volume  of  carbon  dioxide  given  off  is  always  a  little  less  than 
the  volume  of  oxygen  taken  in.  This  seems  to  show  that  some  oxy- 
gen unites  with  some  of  the  chemical  elements  in  the  body. 

Changes  in  the  Blood  within  the  Lungs.  —  Blood,  after  leaving 
the  lungs,  is  much  brighter  red  than  just  before  entering  them. 
The  change  in  color  is  due  to  a  taking  up  of  oxygen  by  the  hcemo- 
glohin  of  the  red  corpuscle.  Changes  taking  place  in  blood  are 
obviously  the  reverse  of  those  which  take  place  in  air  in  the  lungs. 
Blood  in  the  capillaries  within  the  lungs  gains  from  four  to  five  per 
I  ^,.;:i^-_-_v-:rr-— .  1/  ^^^^  ^f  oxygen,  which  the  air  loses. 
~  '^:^}l^5?}^^~-';-^/:<'^'^         At  the  same  time  hlood  loses  the  four 

per  cent  of  carbon  dioxide,  which  the 
air  gains.  The  water,  of  which 
about  half  a  pint  is  given  off  daily, 
is  mostly  lost  from  the  blood. 


a 


Problem  LIU.  J_  study  of  ven- 
tilation. {Laboratory  Manual, 
Froh.  LIII.) 

Need  of  Ventilation.  ■ —  During 
the  course  of  a  day  the  lungs  have 
lost  to  the  surrounding  air  nearly 
two  pounds  of  carbon  dioxide.  This 
means  that  about  three  fifths  of  a 
cubic  foot  is  given  off  from  each 
person  during  an  hour.  When  we 
are  confined  for  some  time  in  a  room, 
it  becomes  necessary  to  get  rid  of 
this  carbon  dioxide.  This  can  be 
done  only  by  means  of  proper  ven- 
tilation. Other  materials  are  passed 
off  from  the  lungs  with  carbon  di- 
oxide. It  is  the  presence  of  these 
wastes  in  combination  with  carbon  dioxide  that  makes  breathed 
air  particularly  unwholesome.  The  presence  of  impurities  in  the 
air  of  a  room  may  easily  be  determined  by  its  odor.  The  close 
smell  of  a  poorly  ventilated  room  is  due  to  organic  impurities 
given  off  with  the  carbon  dioxide.    This,  fortunately,  gives  us  an 


Three  ways  of  ventilating  a  room: 
i,  inlet  for  air  ;  o,  outlet  for  air. 
Which  is  the  best  method  of  ven- 
tilation ?    Explain. 


RESPIRATION   AND   EXCRETION 


387 


index  by  which  we  may  prevent  poisoning.  Air  containing  from 
6  to  8  parts  of  carbon  dioxide  to  10,000  parts  of  air  is  bad ;  while 
from  12  to  14  parts  in  10,000  makes  a  very  dangerous  amount. 
Among  the  factors  which  take  oxygen  from  the  air  in  a  closed 
room  and  produce  carbon  dioxide  are  burning  gas  or  oil  lamps, 
stoves,  the  presence  of  a  number  of  people,  etc. 

Proper  Ventilation.  —  Ventilation  consists  in  the  removal  of 
air  that  has  been  used,  and  the  introduction  of  a  fresh  supply  to 
take  its  place.  If  we  remember  that  warm  air  is  lighter  than  cold 
air,  and  carbon  dioxide  is  heavier  than  air,  we  can  see  that  ventila- 
tion outlets  should  be  on  the  level  of  the  floor.  The  inlets  should 
be  near  the  top  of  the  room,  especially  in  houses  heated  by  any 
method  of  direct  radiation,  such  as  steam  or  hot  water.  A  good 
method  of  ventilation  for  the  home  is  to  place  a  board  two  or  three 
inches  high  between  the 
lower  sash  and  the  frame 
of  a  window.  An  open 
fireplace  in  a  room  aids 
in  ventilation  because  of 
the  constant  draft  up 
the  fluo. 

Sweeping  and  Dusting. 
—  It  is  very  easy  to  dem- 
onstrate the  amount  of 
dust  in  the  air  by  follow- 
ing the  course  of  a  beam 
of  light  in  a  darkened 
room.  We  have  already 
proved    that    spores    of 

mold    and    yeast   exist    in     Plate  culture  exposed  for  five  minutes  in  a  school 

the   air.     That    bacteria      ^^^^  ^^^'^^  p"p^^^  ^^'"^  passing  to  recitations. 

,  .  ,  Each  spot  is  a  colony  of  bacteria  or  mold. 

are  also  present   can  be 

proved  by  exposing   a    sterilized    gelatin   plate  to  the  air  in  a 

schoolroom  for  a  few  moments.^ 


^  Expose  two  sterilized  dishes  containing  culture  media ;    one  in  a  room  being 
swept  with  a  damp  broom,  and  the  other  in  a  room  which  is  being  swept  in  the  usual 


manner.     Note  the  formation  of  colonies  of  bacteria  in  each  dish. 
does  the  most  growth  take  place? 


In  which  dish 


388  RESPIRATION  AND  EXCRETION 

Many  of  the  bacteria  present  in  the  air  are  active  in  causing 
viiseases  of  the  respiratory  tract,  such  as  diphtheria,  membranous 
croup,  and  tuberculosis.  Other  diseases,  as  colds,  bronchitis 
(inflammation  of  the  bronchial  tubes),  and  pneumonia  (inflam- 
mation of  the  tiny  air  sacs  of  the  lungs),  are  probably  caused  by 
bacteria. 

Dust,  with  its  load  of  bacteria,  will  settle  on  any  horizontal  sur- 
face in  a  room  not  used  for  three  or  four  hours.  Dusting  and 
sweeping  should  always  be  done  with  a  damp  cloth  or  broom, 
otherwise  the  bacteria  are  simply  stirred  up  and  sent  into  the  air 
again.  The  proper  watering  of  streets  before  they  are  swept  is 
also  an  important  factor  in  health. 

Ventilation  of  Sleeping  Rooms.  —  Sleeping  in  close  rooms  is 
the  cause  of  much  illness.  Beds  ought  to  be  placed  so  that  a 
constant  supply  of  fresh  air  is  given  without  a  direct  draft.  This 
may  often  be  managed  with  the  use  of  screens.  Bedroom  windows 
should  be  thrown  open  in  the  morning  to  allow  free  entrance  of  the 
sun  and  air,  bedclothes  should  be  washed  frequently,  and  sheets 
and  pillow  covers  often  changed.  Bedroom  furniture  should  be 
simple,  and  but  little  drapery  allowed  in  the  room. 

Hygienic  Habits  of  Breathing.  —  Every  one  ought  to  accustom 
himself  upon  going  into  the  open  air  to  inspire  slowly  and  deeply 
to  the  full  capacity  of  the  lungs.  A  slow  expiration  should  follow. 
Take  care  to  force  the  air  out.  Breathe  through  the  nose,  thus 
warming  the  air  you  inspire  before  it  enters  the  lungs  and  chills 
the  blood.  Repeat  this  exercise  several  times  every  day.  You  will 
thus  prevent  certain  of  the  air  sacs  which  are  not  often  used  from 
becoming  hardened  and  permanently  closed. 

The  Relation  of  Tight  Clothing  to  Correct  Breathing.  —  It  is  im- 
possible to  breathe  correctly  unless  the  clothing  is  worn  loosely 
over  the  chest  and  abdomen.  Tight  corsets  and  tight  belts  prevent 
the  walls  of  the  chest  and  the  abdomen  from  pushing  outward  and 
interfere  with  the  drawing  of  air  into  the  lungs.  They  may  also 
result  in  permanent  distortion  of  parts  of  the  skeleton  directly  under 
the  pressure.  Other  organs  of  the  body  cavity,  as  the  stomach  and 
intestines,  may  be  forced  downward,  out  of  place,  and  in  conse- 
quence do  not  perform  their  work  properly. 

Relation  of  Exercise.  —  We  have  already  seen  that  exercise  re- 


RESPIRATION  AND   EXCRETION  389 

suits  in  the  need  of  greater  food  supply,  and  hence  a  more  rapid 
pumping  of  blood  from  the  heart.  With  this  comes  need  of  more 
oxygen  to  allow  the  oxidations  whit^h  supply  the  greater  energy 
used.  Hence  deeper  breathing  during  time  of  exercise  is  a  prime 
necessity  in  order  to  increase  the  absorbing  surface  of  the  lungs. 

Suffocation  and  Artificial  Respiration.  —  Suffocation  results  from  the 
shutting  off  of  the  supply  of  oxygen  from  the  lungs.  It  may  be  brought 
about  by  an  obstruction  in  the  windpipe,  by  a  lack  of  oxygen  in  the  air, 
by  inhaling  some  other  gas  in  quantity,  or  by  drowning.  A  severe  electric 
shock  may  paralyze  the  nervous  centers  which  control  respiration,  thus 
causing  a  kind  of  suffocation.  In  the  above  cases,  death  often  may  be  pre- 
vented by  prompt  recourse  to  artificial  respiration.  To  accomplish  this, 
place  the  patient  on  his  back  with  the  head  lower  than  the  body ;  grasp 
the  arms  near  the  elbows  and  draw  them  upward  and  outward  until  they 
are  stretched  above  the  head,  on  a  line  with  the  body.  By  this  means  the 
chest  cavity  is  enlarged  and  an  inspiration  produced.  To  produce  an  ex- 
piration, carry  the  arms  downward,  and  press  them  against  the  chest, 
thus  forcing  the  air  out  of  the  lungs.  This  exercise,  regularly  repeated 
every  few  seconds,  if  necessary  for  hours,  has  been  the  souj-ce  of  saving 
many  lives. 

Common  Diseases  of  the  Nose  and  Throat.  —  Catarrh  is  a  disease  which 
people  with  sensitive  mucous  membrane  of  the  nose  and  throat  are  sub- 
ject to.  It  is  indicated  by  the  constant  secretion  of  mucus  from  these 
membranes.  Frequent  spraying  of  the  nose  and  throat  with  some  mild 
antiseptic  solutions  is  found  useful.  Chronic  catarrh  should  be  at- 
tended to  by  a  physician.  Often  we  find  children  breathing  entirely 
through  the  mouth,  the  nose  being  seemingly  stopped  up.  When  this  goes 
on  for  some  time  the  nose  and  throat  should  be  examined  by  a  physician 
for  adenoids,  or  growths  of  soft  masses  of  tissue  which  fill  up  the  nose 
cavity,  thus  causing  a  shortage  of  the  air  supply  for  the  body.  Many  a 
child,  backward  at  school,  thin  and  irritable,  has  been  changed  to  a  healthy, 
normal,  bright  scholar  by  the  removal  of  adenoids.  Sometimes  the 
tonsils  at  the  back  of  the  mouth  cavity  may  become  enlarged,  thus  shut- 
ting off  the  air  supply  and  causing  the  same  trouble  as  we  see  in  a  case  of 
adenoids.  The  simple  removal  of  the  obstacle  by  a  doctor  soon  cures 
this  condition. 

Cell  Respiration.  —  It  has  been  found,  in  the  case  of  very 
simple  animals,  such  as  the  arnceba,  that  when  oxidation  takes 
place  in  a  cell,  work  results  from  this  oxidation.  The  oxygen 
taken  into  the  lungs  is  not  used  there,  but  is  carried  by  the  blood 
to  such  parts  of  the  body  as  need  oxygen  to  oxidize  food  mate- 
rials in  the  cells.     The  quantity  of  oxygen  used  by  the  body  is 


390 


RESPIRATION   AND   EXCRETION 


The  respiration  of  cells. 


nearly  dependent  on  the  amount  of  work  performed.  From 
twenty  to  twenty-five  ounces  is  taken  in  and  used  by  the  body 
every  day.  Oxygen  is  constantly  taken  from  the  blood  by  tis- 
sues in  a  state  of  rest  and  is 
used  up  when  the  body  is  at 
work.  This  is  proved  by  the 
fact  that  in  a  given  time  a 
man,  when  working,  gives  off 
more  oxygen  (in  carbon  di- 
oxide) than  he  takes  in  during 
that  time. 

While  work  is  being  done 
certain  wastes  are  formed  in 
the  cell.  Carbon  dioxide  is 
released  when  carbon  is  burned.  But  when  proteids  are  burned, 
another  waste  product  containing  nitrogen  is  formed.  This  must 
be  passed  off  from  the  cells,  as  it  is  a  poison.  Here  again  the 
blood  and  l^nnph,  common  carriers,  take  the  waste  material  to 
points  where  it  may  be  excreted  or  passed  out  of  the  body. 

Organs  of  Excretion.  —  All  the 
life  processes  which  take  place  in  a 
living  thing  result  ultimately,  in 
addition  to  giving  off  of  carbon  di- 
oxide, in  the  formation  of  organic 
wastes  within  the  body.  Such  or- 
ganic waste  contains  nitrogen,  and 
in  animals  is  usually  called  urea. 
In  man,  the  skin  and  kidneys  per- 
form this  function,  hence  they  are 
called  the  organs  of  excretion. 

The  Human  Kidney.  —  The  hu- 
man kidney  is  about  four  inches 
long,  two  and  one  half  inches  wide, 
and  one  inch  in  thickness.  Its  color 
is  dark  red.  If  the  structure  of  the  medulla  and  cortex  (see  Fig- 
ure above)  is  examined  under  the  compound  microscope,  you 
will  find  these  regions  to  be  composed  of  a  vast  number  of  tiny 
branched  and  twisted  tubules.     The  outer  end  of  each  of  these 


Suprarenal 

body 


Ureter 


Longitudinal  section  of  kidney. 


RESPIRATION  AND   EXCRETION 


391 


tubules  opens  into  the  pelvis,  the  space  within  the  kidney;  the 
inner  end,  in  the  cortex,  forms  a  tiny  closed  sac.  In  each  sac,  the 
outer  wall  of  the  tube  has  grown  inward  and  carried  with  it  a  very 
tiny  artery.  This  artery  breaks  up  into  a  mass  of  capillaries. 
These  capillaries,  in  turn,  unite  to  form  a 
small  vein  as  they  leave  the  little  sac. 
Each  of  these  sacs  with  its  contained 
blood  vessels  is  called  a  glomendus. 

Wastes  given  off  by  the  Blood  in  the 
Kidney.  —  In  the  glomerulus  the  blood 
loses  by  osmosis,  through  the  very  thin 
walls  of  the  capillaries,  first,  a  consider- 
able amount  of  water  (amounting  to 
nearly  three  pints  daily) ;  second,  a  ni- 
trogenous waste  material  known  as  urea ; 
third,  salts  and  other  waste  organic  sub- 
stances, uric  acid  among  them. 


Diagram  of  kidney  circula- 
tion, showing  a  glomerulus 
and  tubule  :  a,  artery  bring- 
ing blood  to  part ;  6,  capil- 
lary bringing  blood  to 
glomerulus ;  6',  vessel  con- 
tinuing with  blood  to  tu- 
bule ;  c,  vein ;  t,  tubule ;  (?, 
glomerulus. 


These  waste  products,  together  with  the 
water  eontaiiiing  them,  are  known  as  urine. 
The  total  amount  of  nitrogenous  waste  leav- 
ing the  body  each  day  is  about  twenty  grams ; 
this  is  nearly  all  accounted  for  in  the  urea 
passed  off  by  the  kidney,  as  urine  is  secreted 
in  the  kidney.  It  is  passed  through  the  ureter 
to  the  urinary  bladder;  from  this  reservoir  it 
is  passed  out  of  the  body,  through  a  tube  called  the  urethra.  After  the 
blood  has  passed  through  the  glomeruli  of  the  kidneys  it  is  purer  than  in 
any  other  place  in  the  body,  because,  before  coming  there,  it  lost  a  large 
part  of  its  burden  of  carbon  dioxide  in  the  lungs.  After  leaving  the  kid- 
ney it  has  lost  much  of  its  nitrogenous  waste.  So  dependent  is  the  body 
upon  the  excretion  of  its  poisonous  material  that,  in  cases  where  the  kid- 
neys do  not  do  their  work  properly,  death  may  ensue  within  a  few  hours. 

Structure  and  Use  of  Sweat  Glands.  —  If  you  examine  the  sur- 
face of  your  skin  with  a  lens,  you  will  notice  the  surface  is  thrown 
into  Httle  ridges.  In  these  ridges  may  be  found  a  large  number 
of  very  tiny  pits;  these  are  the  pores  or  openings  of  the  sweat- 
secreting  glands.  From  each  opening  a  little  tube  penetrates  deep 
within  the  epidermis;  there,  coiling  around  upon  itself  several 
times,  it  forms  the  sweat  gland.     Close  around  this  coiled  tube  are 


392  RESPIRATION  AND  EXCRETION 

found  many  capillaries.  From  the  blood  in  these  capillaries,  cells 
lining  the  wall  of  the  gland  take  water,  and  with  it  a  little  carbon 
dioxide,  urea,  and  some  salts  (common  salt  among  others).  This 
forms  the  excretion  known  as  sweat.  The  combined  secretions 
from  these  glands  amount  normally  to  a  little  over  a  pint  during 
twenty-four  hours.  At  all  times,  a  small  amount  of  sweat  is  given 
off,  but  this  is  evaporated  or  is  absorbed  by  the  underwear;  as 
this  passes  off  unnoticed  it  is  called  insensible  perspiration.  In 
hot  weather  or  after  hard  manual  labor  the  amount  of  perspiration 
is  greatly  increased. 

Relation  of  Bodily  Heat  to  Work  Performed.  —  The  bodily  tem- 
perature of  a  person  engaged  in  manual  labor  will  be  found  to  be 
but  httle  higher  than  the  temperature  of  the  same  person  at  rest. 
When  a  man  works,  he  releases  energy  by  oxidizing  food  material 
or  tissue  in  the  body.  Thus  we  know  from  our  previous  experi- 
ments that  heat  is  released.  Muscles,  nearly  one  half  the  weight  of 
the  body,  release  about  five  sixths  of  their  energy  as  heat.  At  all 
times  they  are  giving  up  some  heat.  How  is  it  that  the  bodily 
temperature  does  not  differ  greatly  at  such  times? 

Regulation  of  Heat  of  the  Body.  —  The  temperature  of  the 
body  is  largely  regulated  by  means  of  the  activity  of  the  sweat 
glands.  The  blood  carries  much  of  the  heat,  liberated  in  the 
various  parts  of  the  body  by  the  oxidation  of  food,  to  the  surface 
of  the  body,  where  it  is  lost  in  the  evaporation  of  sweat.  In  hot 
weather  the  blood  vessels  of  the  skin  are  dilated ;  in  cold  weather 
they  are  made  smaller  by  the  action  of  the  nervous  system.  The 
blood  thus  loses  water  in  the  skin,  the  water  evaporates,  and  we 
are  cooled  off.  The  object  of  increased  perspiration,  then,  is  to  re- 
move heat  from  the  body.  With  a  large  amount  of  blood  present 
in  the  skin,  perspiration  is  increased ;  with  a  small  amount,  it  is 
diminished.  Hence,  we  have  in  the  skin  an  automatic  regulator 
of  bodily  temperature. 

Sweat  Glands  under  Nervous  Control.  —  The  sweat  glands,  like  the 
other  glands  in  the  body,  are  under  the  control  of  the  sympathetic  nervous 
system.  Frequently  the  nerves  dilate  the  blood  vessels  of  the  skin,  thus 
helping  the  sweat  glands  to  secrete,  by  giving  them  more  blood. 

*'  Thus  regulation  is  carried  out  by  the  nervous  system  determining,  on 
the  one  hand,  the  loss  by  governing  the  supply  of  blood  to  the  skin  and  the 


RESPIRATION  AND  EXCRETION  393 

action  of  the  sweat  glands ;  and  on  the  other,  the  production  by  diminish- 
ing or  increasing  the  oxidation  of  the  tissues."  —  Foster  and  Shore,  Physi- 
ology. 

Comparison  with  Cold-blooded  Animals.  —  We  have  seen  the  bodUy 
temperature  of  a  frog  remain  nearly  that  of  the  surrounding  medium. 
Fishes,  all  amphibious  animals,  and  reptiles  are  alike  in  this  respect.  This 
change  in  the  bodily  temperature  is  due  to  the  absence  of  regulation  by  the 
nervous  system.  A  sort  of  regulation  is  exerted,  however,  by  outside  forces, 
for  the  cold  in  winter  causes  the  cold-blooded  animals  to  become  inactive. 
Warm  weather,  on  the  other  hand,  stimulates  them  to  greater  activity  and 
to  increased  oxidation.  This  is  naturally  followed  by  a  rise  in  bodily  tem- 
perature. 

Brohlem  LTV,  J.  final  study  of  changes  in  the  composition 
of  Wood  in  various  parts  of  the  body,  {Laboratory  Manual, 
Prob.  LIV,) 

Summary  of  Changes  in  Blood  within  the  Body.  —  We  have 
already  seen  that  red  corpuscles  in  the  lungs  lose  part  of  their  load 
of  carbon  dioxide  that  they  have  taken  from  the  tissues,  replacing 
it  with  oxygen.  This  is  accompanied  by  a  change  of  color  from 
purple  (in  blood  which  is  poor  in  oxygen)  to  that  of  bright  red  (in 
richly  oxygenated  blood).  Other  changes  take  place  in  other  parts 
of  the  body.  In  the  walls  of  the  food  tube,  especially  in  the  small 
intestine,  the  blood  receives  its  load  of  fluid  food.  In  the  muscles 
and  other  working  tissues  the  blood  gives  up  food  and  oxygen, 
receiving  carbon  dioxide  and  organic  waste  in  return.  In  the  liver, 
the  blood  gives  up  its  sugar,  and  the  worn-out  red  corpuscles  which 
break  down  are  removed  (as  they  are  in  the  spleen)  from  the 
circulation.  In  glands,  it  gives  up  materials  used  by  the  gland 
cells  in  their  manufacture  of  secretions.  In  the  kidneys,  it  loses 
water  and  nitrogenous  wastes  {urea).  In  the  skin,  it  also  loses 
some  waste  materials,  salts,  and  water. 

Hygiene  of  the  Skin.  —  The  skin  as  an  organ  of  excretion  is  of 
importance.  It  is  of  even  greater  importance  as  a  regulator  of 
bodily  temperature.  The  mouths  of  the  sweat  glands  must  not 
be  allowed  to  become  clogged  with  dirt.  The  skin  of  the  entire 
body  should,  if  possible,  be  bathed  daily.  For  those  who  can  stand 
it,  a  cold  sponge  bath  is  best.  Soap  should  be  used  daily  on  parts 
exposed  to  dirt.  Exercise  in  the  open  air  is  important  to  all  who 
<ie§ire  a  good  complexion.    The  body  should  be  kept  at  an  even 


394 


RESPIRATION  AND   EXCRETION 


temperature  by  the  use  of  proper  underclothing.  Wool,  a  poor 
conductor  of  heat,  should  be  used  in  winter,  and  cotton,  which 
allows  of  a  free  escape  of  heat,  in  summer. 

Cuts,  Bruises,  and  Burns.  —  In  case  the  skin  is  badly  broken 
it  is  necessary  to  prevent  the  entrance  and  growth  of  bacteria. 
This  may  be  done  by  washing  the  wound  with  weak  antiseptic 
solutions,  such  as  3  %  carbolic  acid,  S%  lysol,  peroxide  of  hydrogen 
(full  strength),  or  sl  yq%  solution  of  bichloride  of  mercury.  A 
handful  should  be  applied  immediately. 

"  A  burn  or  scald  should  be  covered  at  once  with  a  paste  of  baking 
soda,  which  tends  to  lessen  the  pain  by  keeping  out  the  air  and  reducing 

the  inflammation.  A  mixtm-e  of 
linseed  oil  and  limewater,  known 
as  carron  oil,  is  a  good  remedy  to 
keep  on  hand  for  burns."  —  Pea- 
body,  Physiology. 

Colds    and    Fevers. — The 

regulation  of  blood  passing 
through  the  blood  vessels  is 
under  control  of  the  nervous 
system.  If  this  mechanism  is 
interfered  with  in  any  way, 
the  sweat  glands  may  not  do 
their  work,  perspiration  may 
be  stopped,  and  the  heat  from 
oxidation  held  within  the 
body.  The  body  temperature 
goes  up,  and  a  fever  results. 

If  the  blood  vessels  in  the 
skin  are  suddenly  cooled  when 
full  of  blood,  they  contract 
and  send  the  blood  elsewhere. 
As  a  result  a  congestion  or 
cold  may  follow.     Colds  are, 

in  reality,  a  congestion  of  membranes  lining  certain  parts  of  the 

body,  as  the  nose,  throat,  windpipe,  or  lungs. 

When  suffering  from  a  cold,  it  is  therefore  important  not  to  chijl 

the  skin,  as  a  full  blood  supply  should  be  kept  in  it  and  so  kept 


spgig^^ril 


A,  blood  vessels  in  skin  normal;   B,  when 
congested. 


RESPIRATION  AND   EXCRETION  395 

from  the  seat  of  the  congestion.  For  this  reason  hot  baths  (which 
call  the  blood  to  the  skin),  the  avoiding  of  drafts  (which  chill  the 
skin),  and  warm  clothing  are  useful  factors  in  the  care  of  colds. 

'*  The  Bodily  Heat  as  afifected  by  Alcohol.  —  Alcohol  lowers  the  tem- 
perature of  the  body  by  dilating  the  blood  vessels  of  the  skin.  It  does 
this  by  means  of  its  influence  on  the  nervous  system.  It  is,  therefore, 
a  mistake  to  drink  alcoholic  beverages  when  one  is  extremely  cold,  because 
by  means  of  this  more  bodily  heat  is  allowed  to  escap)e. 

"Because  alcohol  is  quickly  oxidized,  and  because  heat  is  produced 
in  the  process,  it  was  long  believed  to  be  of  value  in  maintaining  the  heat 
of  the  body.  A  different  view  now  prevails  as  the  result  of  much  obser- 
vation and  experiment.  Physiologists  show  by  careful  experiments  that 
though  the  temperature  of  the  body  rises  during  digestion  of  food,  it  is 
lowered  for  some  hours  when  alcohol  is  taken.  The  flush  which  is  felt  upon 
the  skin  after  a  drink  of  wine  or  spirits  is  due  in  part  to  an  increase  of  heat 
in  the  body,  but  also  to  the  paralyzing  effect  of  the  alcohol  upon  the  capil- 
lary walls,  allowing  them  to  dilate,  and  so  permitting  more  of  the  warm 
blood  of  the  interior  of  the  body  to  reach  the  surface.  There  it  is  cooled 
by  radiation,  and  the  general  temperature  is  lowered."  —  Macy,  Physi- 
ology. 

Effect  of  Alcohol  on  Respiration.  —  It  has  been  shown  that  alcohol  tends 
to  congest  the  membranes  of  the  organs  of  respiration.  This  it  does  by 
relaxing  the  membranes  of  the  throat  and  lungs. 

"  Those  who  have  injured  themselves  with  alcohol  show  less  power  of 
resistance  against  influences  unfavorable  to  health,  and  are  carried  off  by 
diseases  which  other  people  of  the  same  age  pass  through  safely,  especially 
in  cases  of  inflammation  of  the  lungs."  —  Birch-Hirschfeld. 

"  The  action  of  alcohol  upon  the  muscular  walls  of  the  arteries,  which 
has  been  already  more  than  once  referred  to,  is  especially  important  in  the 
capillaries  of  the  lungs.  When  they  are  dilated  by  the  paralyzing  effect  of 
alcohol,  their  expansion  reduces  the  size  of  the  air  cells  in  the  lungs  and 
leaves  less  room  for  the  air  which  the  lungs  need,  so  that  less  oxygen  is  sup- 
plied to  the  blood.  When  the  capillaries  are  often  or  continuously  dis- 
tended in  this  way,  their  walls  are  likely  to  become  permanently  thickened, 
and  the  interchange  of  gases  which  normally  takes  place  there,  by  which 
carbon  dioxide  passes  from  the  blood  while  the  purifying  oxygen  is  taken 
into  the  blood,  is  impeded.  Serious  disease  even  may  result,  such  as  a 
peculiar  and  quickly  fatal  form  of  consumption  found  only  among  drinkers 
of  alcoholic  fluids. 

"  Dr.  Legendre,  a  Paris  physician,  has  recently  published,  for  public 
distrihution,  a  leaflet,  in  which  he  says :  '  Alcohol  is  a  frequent  cause  of 
consumption  by  its  power  of  weakening  the  lungs.  Every  year  we  see 
patients  who  attend  the  hospital  for  alcohoUsm  come  back  after  a  period 
to  be  treated  for  consumption.'  "  —  Loudon  Lancet* 


396  RESPIRATION   AND  EXCRETION 

"  An  American  medical  writer  {Journal  of  American  Medical  Asso- 
ciation) points  out  the  reason  why  the  use  of  alcohol  makes  one  liable  to 
consumption.  He  mentions  the  use  of  alcohol  among  various  other  things 
which  cause  the  natural  vital  resistance  of  the  healthy  body  to  be  impaired. 
Among  those  other  things  mentioned  with  alcohol,  which  produce  this 
impairment  of  vital  resistance,  are  :  '  Living  in  overcrowded,  ill- ventilated 
houses,  on  damp  soils,  or  insufficient  clothing  and  outdoor  exercise.'  "  — 
Hall,  Elementary  Physiology. 

"  Alcohol  interferes  with  the  Respiration  of  the  Cells.  —  Alcol^ol  is 
quickly  absorbed  from  the  stomach  and  intestine  and  as  quickly  disap- 
pears. After  it  is  taken,  Uttle  or  no  alcohol,  or  any  substance  like  alcohol, 
or  any  substance  containing  so  little  oxygen  as  alcohol,  can  be  found  in  any 
waste  of  the  body.  Hence  the  inference  is  that  it  must  be  oxidized,  al- 
though the  exact  point  and  the  manner  of  its  oxidation  may  not  be  known. 
But  the  evidence  for  its  oxidation  is  the  same  as  that  for  the  oxidation  of 
sugar. 

"  Every  ounce  of  alcohol  requires  nearly  two  ounces  of  oxygen  to 
oxidize  it  fully.  Taking  twenty-five  ounces  of  oxygen  gas  as  the  amount 
used  in  a  day,  there  will  be  only  one  ounce  used  in  an  hour.  So  to  oxidize 
an  ounce  of  alcohol  takes  an  amount  of  oxygen  equal  to  the  whole  supply 
of  the  body  for  two  hours.  Three  or  four  drinks  of  whisky  contain  this 
ounce  of  alcohol.  If  this  amount  is  drunk,  there  will  soon  be  a  lessened 
action  and  a  narcotic  effect  throughout  the  body,  due  mainly  to  the 
lack  of  oxygen.  A  noticeable  degree  of  uncertain  action  is  called  intoxi- 
cation. 

"  Using  alcohol  in  the  body  is  like  burning  kerosene  in  a  coal  stove. 
By  taking  great  care  a  little  kerosene  can  be  made  to  give  out  some  heat 
from  the  stove,  but  the  operation  is  dangerous.  Some  people  seem  to 
oxidize  alcohol  within  the  body  with  but  little  harm ;  but  they  run  great 
risks  of  doing  themselves  harm,  and  the  result  is  not  nearly  so  good  as  if 
they  had  used  proper  food. 

"  Effects  of  Tobacco  on  Respiration.  —  Tobacco  smoke  contains  the 
same  kind  of  poisons  as  the  tobacco,  with  other  irritating  substances 
added.  It  is  usually  sucked  into  the  mouth  and  at  once  blown  out  again, 
but  cigarette  smoke  is  commonly  drawn  into  the  lungs  and  afterwards 
blown  out  through  the  nose.  It  is  irritating  to  the  throat,  causing  a 
cough  and  rendering  it  more  liable  to  inflammation.  If  inhaled  into  the 
bronchi,  it  produces  still  greater  irritation,  and  the  vaporized  nicotine  is 
more  readily  absorbed  if  the  smoke  is  inhaled  the  more  deeply.  Cigarettes 
contain  the  same  poisons  as  other  forms  of  tobacco,  and  often  contain 
other  poisons  which  are  added  to  flavor  them."  —  Overton,  Applied 
Physiology. 

"  The  throat,  bronchial  tubes,  and  lungs  of  a  tobacco  smoker  are  all 
liable  to  irritation  by  the  poisonous  smoke,  and  chronic  inflammation  is 
often  caused.     The  nicotine  of  tobacco  is  a  deadly  poison,  and  in  cigarettes 


RESPIRATION  AND   EXCRETION  397 

there  are  often  other  poisons  equally   dangerous  to  health."  —  Macy, 
Physiology. 

Effect  of  Alcohol  on  the  Kidneys.  —  It  is  said  that  alcohol  is  one  of 
the  greatest  causes  of  disease  in  the  kidneys.  The  forms  of  disease  known 
as  "  fatty  degeneration  of  the  kidney  "  and  "  Bright's  disease  "  are  both 
frequently  due  to  this  cause.  The  kidneys  are  the  most  important  or- 
gans for  the  removal  of  nitrogenous  waste. 

Alcohol  unites  more  easily  with  oxygen  than  most  other  food  materials, 
hence  it  takes  away  oxygen  that  would  otherwise  be  used  in  oxidizing  these 
foods.  Imperfect  oxidation  of  foods  causes  the  development  and  reten- 
tion of  poisons  in  the  blood  which  it  becomes  the  work  of  the  kidneys  to 
remove.  If  the  kidneys  become  overworked,  disease  will  occur.  Such 
disease  is  likely  to  make  itself  felt  as  rheumatism  or  gout,  both  of  which 
are  believed  to  be  due  to  waste  products  (poisons)  in  the  blood. 

Dr.  McMichael,  in  the  Dietetic  and  Hygienic  Gazette,  says,  "  Alcohol 
produces  disease  of  the  liver  and  of  the  kidneys  because  these  glands  are 
most  concerned  in  the  throwing  out  of  any  poison,  and  are  always,  until 
they  are  deranged  in  structure,  engaged  in  removing  it  from  the  body." 
He  further  says  that  the  disease  almost  universally  caused  in  the  liver  by 
alcohol  is  one  in  which  the  connective  tissue  framework  of  the  liver  in- 
creases, taking  the  place  of  the  liver  cells,  until  the  liver  is  no  longer  able 
to  perform  its  function. 

The  kidneys  may  undergo  a  change  similar  to  that  of  the  liver  when 
alcohol  is  used,  even  in  moderate  amounts,  for  a  long  {)eriod. 

*'  Influence  of  Alcohol  upon  Excretion.  —  If  the  waste  substances  con- 
stantly formed  in  the  body  are  not  promptly  removed,  they  tend  to  poison 
the  system.  When  the  organism  is  at  a  high  level  of  health,  the  breaking 
down  of  tissue  by  oxidation,  which  produces  waste,  goes  on  rapidly  and 
vigorously.  When  this  is  retarded,  as  we  have  seen  it  to  be  when  alcohol 
is  introduced  into  the  circulation  and  uses  up  the  oxygen  which  should 
be  applied  to  the  oxidation  of  food,  then  the  weight  may  increase,  but  it  is 
by  the  retention  of  poisonous  matter  which  ought  to  be  removed.  No 
other  one  cause  creates  so  much  disease  of  the  kidneys  as  does  the  use  of 
alcohol.  Imperfect  oxidation  of  food  develops  poisons  which  the  kidneys 
are  overtaxed  to  remove.  This  may  be  caused  by  eating  too  much,  or 
by  eating  unwholesome  food,  or  too  much  of  certain  kinds  of  food,  as  sugar 
especially ;  or  it  may  be  caused  by  alcohol.  '  Fatty  degeneration  of  the 
kidneys  '  is  a  frequent  result  of  the  use  of  alcoholic  drinks.  The  cells  of 
the  tissues  become  so  altered,  also,  that  they  fail  to  act  normally  by  re- 
moving only  the  poisonous  substances,  and  they  allow  the  valuable  ele- 
ments in  the  blood  to  be  drained  off  with  the  waste.  This  is  seen  in  the 
serious  disease  called  '  Bright's  disease  '  in  which  the  albumin  which  is 
necessary  to  health  is  excreted  by  the  kidneys."  —  Macy,  Physiology. 

Poisons  produced  by  Alcohol.  —  When  too  little  oxygen  enters  the 
draft  of  the  stove,  the  wood  is  burned  imperfectly,  and  there  are  clouds 


398  RESPIRATION  AND  EXCRETION 

of  smoke  and  irritating  gases.  So,  if  oxygen  goes  to  the  alcohol  and  too 
little  reaches  the  cells,  instead  of  carbonic  acid  gas,  and  water,  and  urea 
being  formed,  there  are  other  products,  some  of  which  are  exceedingly 
poisonous  and  which  the  kidneys  handle  with  difficulty.  The  poisons 
retained  in  the  circulation  never  fail  to  produce  their  poisonous  effects, 
as  shown  by  headaches,  clouded  brain,  pain,  and  weakness  of  the  body. 
The  word  "intoxication"  means  'in  a  state  of  poisoning.'  These  poisons 
gradually  accumulate  as  the  alcohol  takes  oxygen  from  the  cells.  The 
worst  effects  come  last,  when  the  brain  is  too  benumbed  to  judge  fairly 
of  their  harm.  It  is  not  true  that  alcohol  in  a  small  amount  is  beneficial. 
A  little  is  too  much,  if  it  takes  oxygen  which  would  otherwise  be  available 
to  oxidize  wholesome  food. 


XXVIII.   THE   NERVOUS  SYSTEM  AND  ORGANS  OF  SENSE 


Problem  LV,     A  study  of  the  nervous  system,  re<ictwns  to 
stimuli,  and  habit  formation.    {.Laboratory  Manual,  Prob.  L  V,) 

Divisions  of  the  Nervous  System.  —  The  control  of  a  number  of 
activities  for  the  attainment  of  a  definite  end  is  the  function  of  the 
nervous  system  in  the  lowest  as  well  as  the  highest  of  animals. 
In  the  vertebrate  animals,  the  nervous  system  consists  of  two 
divisions.  One  includes  the  brain,  spinal  cord,  the  cranial  and 
spinal  nerves,  which  together  make  up  the  cerebrospinal  nervous 
system.  The  other  division  is  called  the  sympathetic  nervous  sys- 
tem. The  activities  of  the  body  are  controlled  from  nerve  centers 
by  means  of  fibers  which  extend  to  all  parts  of  the  body,  there 
ending  in  the  muscles.  The  brain  and  spinal  cord  are  examples 
of  such  centers,  since  they  are  largely  made  up  of  nerve  cells. 
Small  collections  of  nerve  cells,  called  gangliay  are  found  in  other 
parts  of  the  body.  These  nerve  centers  are  connected,  to  a  greater 
or  less  degree,  with  the  surface  of  the  body  by  the  nerves  which 
serve  as  pathways  between  the 
end  organs  of  touch,  sight,  taste, 
etc.,  and  the  centers  in  the  brain 
or  spinal  cord.  Thus  sensation  is 
obtained. 


Nerve  Cells  and  Fibers.  —  A  nerve 
cell,  like  other  cells  in  the  body,  is  a 
mass  of  protoplasm  containing  a  nu- 
cleus. But  the  body  of  the  nerve  cell 
is  usually  rather  irregular  in  shape, 
and  distinguished  from  most  other  cells 
by  possessing  several  delicate,  branched 
protoplasmic  projections  called  den- 
drites. One  of  these  processes,  the 
axis  cylinder  process,  is  much  longer 
than  the  others  and  ends  in  a  muscle 


A  nerve  cell  from  the  brain  of  a 
monkey,  showing  a  great  number 
of  tiny  protoplasmic  projections 
or  dendrites. 


The  central  cerebro-spinal  nervous  system. 


400 


THE  NERVOUS  SYSTEM  AND  ORGANS  OF  SENSE    401 


-.-•TVndHle* 


L\  tl  Body 


■Neuraxon 


■Medulla 


—Node  of  RanvUr 
•Neurilemma 


or  organ  of  sensation.  The  axis  cylinder  process 
forms  the  pathway  over  which  nervous  impulses 
travel  to  and  from  the  nerve  centers. 

A  nerve  consists  of  a  bundle  of  such  tiny  axis 
cylinder  processes,  bound  together  by  a  connec- 
tive tissue.  As  a  nerve  ganglia  is  a  center  of 
activity  in  the  nervous  system,  so  a  nerve  cell 
is  a  center  of  activity  which  may  send  an  impulse 
over  this  thin  strand  of  protoplasm  (the  axis 
cylinder  process)  prolonged  into  a  nerve  fiber 
many  hundreds  of  thousands  of  times  the  length 
of  the  cell.  Some  nerve  cells  in  the  human  body, 
although  visible  only  under  the  compound  micro- 
scope, give  rise  to  axis  cylinder  processes  several 
feet  in  length. 

Because  some  nerve  fibers  originate  in  organs 
that  receive  sensations  and  send  those  sensations 
to  the  central  nervous  system,  they  are  called 
sensory  nerves.  Other  axis  cylinder  processes 
originate  in  the  central  nervous  system  and  pass 
outward  as  nerve  fibers;  such  nerves  produce 
movement  of  muscles  and  are  called  motor  nerves. 

The  Brain  of  Man.  —  In  man,  as  in  the  frog, 
the  central  nervous  system  consists  of  a  brain 
and  spinal  cord  inclosed  in  a  bony  case  with  the 
nerves  leaving  it.     From  the  brain,  twelve  pairs  of  nerves  are  given  off ; 


Nerve-€nds 


Diagram  of  a  neuron  or 
nerve  unit. 


Cerebrxun 


Cerebellum  — 


Medulla 


The  brain,  with  parts  separated  to  show  each  clearly. 
HUNT-   ES.   BIO.  —  26 


402    THE  NERVOUS  SYSTEM  AND  ORGANS  OF  SENSE 

thirty-one  more  leave  the  spinal  cord.  The  brain  has  three  divisions. 
The  cerebrum  makes  up  the  largest  part.  In  this  respect  it  differs  from  the 
cerebrum  of  the  frog  and  other  vertebrates.  It  is  divided  into  two  lobes, 
the  hemispheres,  which  are  connected  with  each  other  by  a  broad  band 
of  nerve  fibers.  The  outer  surface  of  the  cerebrum  is  thrown  into  folds  or 
convolutions.  The  outer  layer,  seen  in  section,  is  gray  in  color,  and  is  made 
up  of  nerve  cells  and  supporting  material  (the  neuroglia,  a  kind  of  connective 
tissue).  The  inner  part  (white  in  color)  is  composed  largely  of  fibers  which 
pass  to  other  parts  of  the  brain  and  down  into  the  spinal  cord.  Under 
the  cerebrum,  and  dorsal  to  it,  lies  the  little  brain,  or  cerebellum.  The 
two  sides  of  the  cerebellum  are  connected  by  a  band  of  nerve  fibers  which 
run  around  into  the  lower  hindbrain  or  medulla.  This  band  of  fibers  is 
called  the  pons.  The  medulla  is,  in  structure,  part  of  the  spinal  cord,  and 
is  made  up  largely  of  fibers  running  longitudinally. 

Sensory  and  Motor  Nerve  Fibers.  —  Nerves  which  are  connected  with 
the  central  nervous  system  may  be  made  up  of  fibers  bearing  messages 
from  sense  organs  in  the  skin  or  elsewhere  to  the  central  nervous  system, 
the  sensory  fibers,  or  of  other  fibers  which  carry  impulses  from  the 
central  nervous  system  to  the  outside,  the  motor  fibers.  Some  nerves 
are  made  up  of  both  kinds  of  fibers,  in  which  case  they  are  called  mixed 
nerves. 

The  Sympathetic  Nervous  System.  —  The  sympathetic  nervous  system 
consists  of  a  series  of  ganglia  connected  with  each  other  and  with  the  cen- 
tral nervous  system  through  some  of  the  spinal  and  cranial  nerves,  espe- 
cially the  vagus  (tenth  cranial).  The  sympathetic  system,  both  in  the  frog 
and  man,  controls  the  muscles  of  the  digestive  tract  and  blood  vessels,  the 
secretions  of  gland  cells,  and  all  functions  which  have  to  do  with  life  pro- 
cesses in  the  body. 

Functions  of  the  Parts  of  the  Central  Nervous  System  of  the  Frog.  — 
From  careful  study  of  living  frogs,  birds,  and  some  mammals  we  have 
learned  much  of  what  we  know  of  the  functions  of  the  parts  of  the  central 
nervous  system  in  man. 

It  has  been  found  that  if  the  entire  brain  of  a  frog  is  destroyed  and 
separated  from  the  spinal  cord,  "  the  frog  will  continue  to  live  but  with  a 
very  peculiarly  modified  activity."  It  does  not  appear  to  breathe,  nor  does 
it  swallow.  It  will  not  move  or  croak,  but  if  acid  is  placed  upon  the  skin 
so  as  to  irritate  it,  the  legs  make  movements  to  push  away  and  to  clean  off 
the  irritating  substance.  The  spinal  cord  is  thus  shown  to  be  a  center  for 
defensive  movements.  If  the  forebrain  is  separated  from  the  rest  of  the 
nervous  system,  the  frog  seems  to  act  a  little  differently  from  the  normal 
animal.  It  jumps  when  touched,  and  swims  when  placed  in  water.  It  will 
croak  when  stroked,  or  swallow  if  food  be  placed  in  its  mouth.  But  it 
manifests  no  hunger  or  fear,  and  is  in  every  sense  a  machine  which  wiU 
perform  certain  actions  after  certain  stimulations.  Its  movements  are 
automatic.     If  now  we  watch  the  movements  of  a  frog  which  has  the  brain 


THE  NERVOUS  SYSTEM  AND  ORGANS  OF  SENSE;    403 


uninjured  in  any  way,  we  find  that  the  frog  acts  spontaneously.  It  tries  to 
escape  when  caught.  It  feels  hungry  and  seeks  food.  It  is  capable  of 
voluntary  action.     It  acts  like  a  normal  individual. 

Functions  of  the  Cerebrum.  —  In  general,  the  functions  of  the 
different  parts  of  the  brain  in  man  agree  with  those  functions 
we    have    already    ob-  ptrfiiori 

served  in  the  frog.    The  ***  — 

cerebrum  has  to  do  with 
conscious  activity;  that 
is,  thought.  It  presides 
over  what  we  call  our 
thoughts,  our  will,  and 
our  sensations.  Each 
part  of  the  area  of  the 
outer  layer  of  the  cere- 
brum is  given  over  to 
some  one  of  the  differ- 
ent functions  of  speech, 
hearing,  sight,  touch, 
movements  of  bodily 
parts.  The  movement 
of  the  smallest  part  of 

the  body  has  its  definite     Regions  of  the  head  and  action  of  the  different 

localized   center  in  the  P^^  of  the  brain, 

cerebrum.  Experiments  have  been  performed  on  monkeys,  and 
these,  together  with  observations  made  on  persons  who  had  lost 

the  power  of  move- 
ment of  certain  parts 
of  the  body,  and 
who,  after  death, 
were  found  to  have 
had  diseases  localized 
in  certain  parts  of  the 
cerebrum,  have  given  to  us  our 
knowledge  on  this  subject. 

Reflex  Actions ;  their  Meaning. — 
Diagram  of  the  path  of  a  simple  ^^    tlirough    disease    or    for    other 

reasons    the    cerebrum    does    not 


nervous  reflex  action. 


404    THE  NERVOUS  SYSTEM  AND  ORGANS  OF  SENSE 

function,  no  will  power  is  exerted,  nor  are  intelligent  acts 
performed.  All  acts  performed  in  such  a  state  are  known  as 
reflex  actions.  An  example  of  a  reflex  may  be  obtained  by  cross- 
ing the  legs  and  hitting  the  knee  a  sharp  blow.  The  leg,  below 
the  knee,  will  fly  up  as  a  result  of  reflex  stimulation.  The 
involuntary  brushing  of  a  fly  from  the  face,  or  the  attempt  to 
move  away  from  the  source  of  annoyance  when  tickled  with  a 
feather,  are  other  examples.  In  a  reflex  act,  a  person  does  not 
think  before  acting.  The  nervous  impulse  comes  from  the  out- 
side to  cells  that  are  not  in  the  cerebrum.  The  message  is  short- 
circuited  back  to  the  surface  by  motor  nerves,  without  ever  having 
reached  the  thinking  centers.  The  nerve  cells  which  take  charge 
of  such  acts  are  located  in  the  cerebellum  or  spinal  cord. 

Automatic  Acts.  —  Some  acts,  however,  are  learned  by  conscious 
thought,  as  writing,  walking,  running,  or  swimming.  Later  in 
life,  however,  these  activities  become  automatic.  The  actual 
performance  of  the  action  is  then  taken  up  by  the  cerebellum, 
medulla,  and  spinal  ganglia.  Thus  the  thinking  portion  of  the 
brain  is  relieved  of  part  of  its  work. 

Habit  Formation.  —  The  training  of  the  different  areas  in  the 
cerebrum  to  do  their  work  well  is  the  object  of  education.  When 
we  learned  to  write,  we  exerted  conscious  effort  in  order  to  make 
the  letters.  Now  the  act  of  forming  the  letters  is  done  without 
thought.  By  training,  the  act  has  become  automatic.  In  the 
beginning,  a  process  may  take  much  thought  and  many  trials 
before  we  are  able  to  complete  it.  After  a  little  practice,  the  same 
process  may  become  almost  automatic.  We  have  formed  a  habit. 
Habits  are  really  acquired  reflex  actions.  They  are  the  result  of 
nature's  method  of  training.  The  conscious  part  of  the  brain  has 
trained  the  cerebellum  or  spinal  cord  to  do  certain  things  that,  at 
first,  were  taken  charge  of  by  the  cerebrum. 

Importance  of  forming  Right  Habits.  —  Among  the  habits  early 
to  be  acquired  are  the  habits  of  studying  properly,  of  concentrat- 
ing the  mind,  of  learning  self-control,  and  above  all,  of  content- 
ment. Get  the  most  out  of  the  world  about  you.  Remember 
that  the  immediate  effect  in  the  study  of  some  subjects  in  school 
may  not  be  great,  but  the  cultivation  of  correct  methods  of  think- 
ing may  be  of  the  greatest  importance  later  in  life. 


THE  NERVOUS  SYSTEM  AND  ORGANS  OF  SENSE    405 

*'  The  hell  to  be  endured  hereafter,  of  which  theology  tells,  is  no  worse 
than  the  hell  we  make  for  ourselves  in  this  world  by  habitually  fashioning 
our  characters  in  the  wrong  way.  Could  the  young  but  realize  how  soon 
they  will  become  mere  walking  bundles  of  habits,  they  would  give  more 
heed  to  their  conduct  while  in  the  plastic  state.  We  are  spinning  our 
own  fates,  good  or  evil,  and  never  to  be  undone.  Every  smallest  stroke 
of  virtue  or  of  vice  leaves  its  never-so-little  scar.  The  drunken  Rip  Van 
Winkle,  in  Jefferson's  play,  excuses  himself  for  every  fresh  dereliction  by 
saying,  *  I  won't  count  this  time ! '  Well !  he  may  not  count  it,  and  a 
kind  Heaven  may  not  count  it;  but  it  is  being  counted  none  the  less. 
Down  among  his  nerve  cells  and  fibers  the  molecules  are  counting  it,  regis- 
tering and  storing  it  up  to  be  used  against  him  when  the  next  temptation 
comes.  Nothing  we  ever  do  is,  in  strict  scientific  literalness,  wiped  out. 
Of  course  this  has  its  good  side  as  well  as  its  bad  one.  As  we  become  per- 
manent drunkards  by  so  many  separate  drinks,  so  we  become  saints  in  the 
moral,  and  authorities  in  the  practical  and  scientific,  spheres  by  so  many 
separate  acts  and  hours  of  work.  Let  no  youth  have  any  anxiety  about 
the  upshot  of  his  education,  whatever  the  line  of  it  may  be.  If  he  keep 
faithfully  busy  each  hour  of  the  working  day,  he  may  safely  leave  the  final 
result  to  itself.  He  can  with  perfect  certainty  count  on  waking  up  some 
fine  morning,  to  find  himself  one  of  the  competent  ones  of  his  generation, 
in  whatever  pursuit  he  may  have  singled  out."  —  James,  Psychology. 

Necessity  of  Food,  Fresh  Air,  and  Rest.  —  The  nerve  cells,  like 
all  other  cells  in  the  body,  are  continually  wasting  away  and  being 
rebuilt.  Oxidation  of  food  material  is  more  rapid  when  we  do 
mental  work.  The  cells  of  the  brain,  like  muscle  cells,  are  not 
only  capable  of  fatigue,  but  show  this  in  changes  of  form  and  of 
contents.  Food  brought  to  them  in  the  blood,  plenty  of  fresh 
air,  especially  when  engaged  in  active  brain  work,  and  rest  at 
proper  times,  are  essential  in  keeping  the  nervous  system  in  con- 
dition. One  of  the  best  methods  of  resting  the  brain  cells  is  a 
change  of  occupation.  Tennis,  golf,  baseball,  and  other  outdoor 
sports  combine  muscular  exercise  with  brain  activity  of  a  different 
sort  from  that  of  business  or  school  work. 

Necessity  of  Sleep/ —  Sleep  is  an  essential  factor  in  the  health  of 
the  brain,  especially  for  growing  children.  Most  brain  cells  attain 
their  growth  early  in  life.  Changes  occur,  however,  until  some 
time  after  the  school  age.  Ten  hours  of  sleep  should  be  allowed 
for  a  child,  and  at  least  eight  hours  for  an  adult.  At  this  time, 
only,  do  the  brain  cells  have  opportunity  to  rest  and  store  food  and 
energy  for  their  working  period. 


406    THE  NERVOUS  SYSTEM  AND  ORGANS  OF  SENSE 


The  Senses 


Touch.  —  In  animals  having  a  hard  outside  covering,  such  as  certain 
worms,  insects,  and  crustaceans,  minute  hairs,  which  are  sensitive  to  touch, 
are  found  growing  out  from  the  body  covering.  At  the  base  of  these  hairs 
are  found  nerve  cells  which  send  a  nerve  fiber  inward  to  the  central  nerv- 
ous system. 

Organs  of  Touch.  —  In  man,  the  nervous  mechanism  which  governs 
touch  is  located  in  the  folds  of  the  dermis  or  in  the  skin.     Special  nerve 

endings,  called  the  tactile  cor- 
-puscles,  are  found  there,  each 
inclosed  in  a  sheath,  or  capsule, 
of  connective  tissue.  Inside  is 
a  complicated  nerve  ending,  and 
nerve  fibers  pass  inward  to  the 
central  nervous  system.  The 
number  of  tactile  corpuscles  pres- 
ent in  a  given  area  of  the  skin 
determines  the  accuracy  and  ease 
with  which  objects  maybe  known 
by  touch. 

If  you  test  the  different  parts 
of  the  body,  as  the  back  of  the 
hand,  the  neck,  the  skin  of  the 
arm,  of  the  back,  or  the  tip  of 
the  tongue,  with  a  pair  of  open 
dividers,  a  vast  difference  in  the  accuracy  with  which  the-  two  points 
may  be  distinguished  is  noticed.  On  the  tip  of  the  tongue,  the  two  points 
need  only  be  separated  by  2V  of  an  inch  to  be  so 
distinguished.  In  the  small  of  the  back,  a  dis- 
tance of  2  inches  may  be  reached  before  the 
dividers  feel  like  two  points. 

Temperature,  Pressure,  Pain.  —  The  feeling 
of  temperature,  pressure,  and  pain,  is  determined 
by  different  end  organs  in  the  skin.  Two  kinds 
of  nerve  fibers  exist  in  the  skin,  which  give  distinct 
sensations  of  heat  and  cold.  These  areas  can  be 
located  by  careful  experimentation.  There  are 
also  areas  of  nerve  endings  which  are  sensitive  to 
pressure,  and  still  others,  most  numerous  of  all, 
sensitive  to  pain. 

Taste  Organs.  —  The  surface  of  the  tongue  is 
folded  into  a  number  of  little  projections  known 
as  papillae.     These  may  be  more  easily  found  on  your  own  tongue  if  a 
drop  of  vinegar  is  placed  on  its  broad  surface.     In  the  folds,  between 


Nerves  in  the  skin  :  a,  nerve  fiber ;  h,  tactile 
papillae,  containing  a  tactile  corpuscle ;  c, 
papillae  containing  blood  vessels.  (After 
Benda.) 


Taste  Cells 


A,  isolated  taste  bud, 
from  whose  upper  free 
end  project  the  ends  of 
the  taste  cells;  B,  sup- 
porting or  protecting 
cell ;   C  sensory  cell. 


THE  NERVOUS  SYSTEM  AND  ORGANS  OF  SENSE    407 

these  projections  on  the  top  and  back  part  of  the  tongue,  are  located 
the  organs  of  taste.     These  organs  are  called  taste  buds. 

Each  taste  bud  consists  of  a  collection  of  spindle-shaped  nerve  cells, 
each  cell  tipped  at  its  outer  end  with  a  hairlike  projection.  These  cells 
send  inward  fibers  to  other  cells,  the  fibers  from  which  ultimately  reach 
the  brain.  The  sensory  cells  are  surrounded  by  a  number  of  protecting 
cells  which  are  arranged  in  layers  about  them.  Thus  the  organ  in  longi- 
tudinal section  looks  somewhat  like  an  onion  cut  lengthwise. 

How  we  Taste.  -—  Four  kinds  of  substances  may  be  distinguished  by 
the  sense  of  taste.  These  are  sweet,  sour,  bitter,  and  salt.  Certain  taste 
cells  located  near  the  back  of  the 

tongue    are    stimulated    only    by    a  /!^  ^t^^^^^:/^-^:^iW^  /!?^^^aa 

bitter  taste.     Sweet   substances  are 
perceived  by  cells  near  the  tip  of  the 
tongue,   sour   substances    along    the     ^'"^**" 
sides,  and  salt  about  equally  all  over 
the  surface.     A  substance  must  be 

dissolved  in  fluid  in  order  to  be  tasted.  ^Nerves 

Many  things   which  we    believe  we         ggction  of  circumvallate  papilla, 
taste  are  in  reality  perceived  by  the 

sense  of  smell.  Such  are  spicy  sauces  and  flavors  of  meats  and  vege- 
tables. This  may  easily  be  proved  by  holding  the  nose  and  chewing, 
with  closed  eyes,  several  diflferent  substances,  such  as  an  apple,  an  onion, 
and  a  raw  potato. 

Smell.  —  The  sense  of  smell  is  located  in  the  membrane  lining  the  upper 
part  of  the  nose.  Here  are  found  a  large  number  of  rod-shaped  cells  which 
are  connected  with  the  forebrain  by  means  of  the  olfactory  nerve.  In 
order  to  perceive  odors,  it  is  necessary  to  have  them  diffused  in  the  air ; 
hence  we  sniff  so  as  to  draw  in  more  air  over  the  olfactory  cells. 

The  Organ  of  Hearing.  —  The  organ  of  hearing  is  the  ear.  In  the  fish, 
frog,  and  reptile,  the  outer  ear,  so  prominent  in  man,  is  entirely  lacking. 
The  outer  ear  consists  of  a  funnel-like  organ  composed  largely  of  cartilage 
which  is  of  use  in  collecting  sound  waves.  This  part  of  the  ear  incloses  the 
auditory  canal,  which  is  closed  at  the  inner  end  by  a  tightly  stretched  mem- 
brane, the  tympanic  membrane.  We  have  seen  the  tympanic  membrane 
of  the  frog  on  the  outer  surface  of  the  head.  The  function  of  the  tympanic 
membrane  is  to  receive  sound  waves,  for  all  sound  is  caused  by  vibrations 
in  the  air,  these  vibrations  being  transmitted,  by  the  means  of  a  com- 
plicated apparatus  found  in  the  middle  ear,  to  the  real  organ  of  hearing 
located  in  the  inner  ear. 

Middle  Ear.  —  The  middle  ear  in  man  is  a  cavity  inclosed  by  the  tem- 
poral bone,  and  separated  from  the  outer  ear  by  the  tympanic  membrane. 
A  little  tube  called  the  Eustachian  tube  connects  the  inner  ear  with  the 
mouth  cavity.  By  allowing  air  to  enter  from  the  mouth,  the  air  pressure 
is  equalized  on  the  ear  drum.     For  this  reason,  we  open  the  mouth  at  the 


408    THE  NERVOUS  SYSTEM  AND  ORGANS  OF  SENSE 


ESC. 

'\ES.C. 


time  of  a  heavy  concussion  and  thus  prevent  the  rupture  of  the  delicate 
tympanic  membrane.  Placed  directly  against  the  tympanic  membrane 
and  connecting  it  with  another  membrane,  separating  the  middle  from 
the  inner  ear,  is  a  chain  of  three  tiny  bones,  the  smallest  bones  of  the  body. 
The  outermost  is  called  the  hammer;  the  next  the  incus,  or  anvil;  the 
third  the  stirrup.  All  three  bones  are  so  called  from  their  resemblances 
in  shape  to  the  articles  for  which  they  are  named.     These  bones  are  held 

in  place  by  very  small 
muscles  which  are  deli- 
cately adjusted  so  as 
to  tighten  or  relax  the 
membranes  guarding 
the  middle  and  inner 
ear. 

The  Inner  Ear.  — 
The  inner  ear  is  one 
of  the  most  compli- 
cated, as  well  as  one 
of  the  most  delicate, 
organs  of  the  body. 
Deep  within  the  tem- 
poral bone  there  are 
found  two  parts,  one 
of  which  is  called,  col- 
lectively, the  semicir- 
cular canal  region,  the 
other  the  cochlea,  or 
organ  of  hearing.  Both 
of  these  organs  consist 
of  membranous  bags  lying  in  a  fluid  which  partially  fills  the  bony  cavity 
which  incloses  them.  These  membranous  structures  themselves  also  con- 
tain a  fluid.  The  semicircular  canals  are  connected  with  the  cochlea  on  one 
side,  and  are  separated  from  the  middle  ear  only  by  a  membrane  and  the 
fluid  which  surrounds  them.  There  are  three  semicircular  canals,  delicate 
membranous  bags  lying  in  a  watery  fluid  and  surrounded  by  bone. 

It  has  been  discovered  by  experimenting  with  fish,  in  which  the  semi- 
circular canal  region  forms  the  chief  part  of  the  ear,  that  this  region  has 
to  do  with  the  equilibrium  or  balancing  of  the  body.  We  gain  in  part  our 
knowledge  of  our  position  and  movements  in  space  by  means  of  the  semi- 
circular canals. 

That  part  of  the  ear  which  receives  sound  waves  is  known  as  the  cochlea, 
or  snail  shell,  because  of  its  shape.  This  very  complicated  organ  is  lined 
with  sensory  cells  provided  with  cilia.  The  cavity  of  the  cochlea  is  filled 
with  a  fluid.  It  is  believed  that  somewhat  as  a  stone  thrown  into  water 
causes  ripples  to  emanate  from  the  spot  where  it  strikes,  so  sound  waves 


•J7.M: 


Section  of  ear  :  E.M.,  auditory  canal ;  Ty.M.,  tympanic 
membrane  ;  Eu.,  Eustachian  tube  ;  Ty,  middle  ear  ; 
Coc,  A.S.C.,  E.S.C.,  etc.,  internal  ear. 


THE  NERVOUS  SYSTEM  AND  ORGANS  OF  SENSE    409 


are  transmitted  by  means  of  the  fluid  filling  the  cavity  to  the  sensory  cells  of 
the  cochlea  (collectively  known  as  the  organ  of  Corti)  and  thence  to  the  brain 
by  means  of  the  auditory  nerve. 

The  Character  of  Sound.  —  When  vibrations  which  are  received  by  the 
ear  follow  each  other  at  regular  intervals,  the  sound  is  said  to  be  musical. 
If  the  vibrations  come  irregularly,  we  call  the  sound  a  noise.  If  the  vibra^ 
tions  come  slowly,  the  pitch  of  the  sound  is  low ;  if  they  come  rapidly,  the 
pitch  is  high.  The  ear  is  able  to  perceive  as  low  as  thirty  vibrations  per 
second  and  as  high  as  almost  thirty  thousand.  The  ear  can  be  trained  to 
recognize  sounds  which  are  unnoticed  in  untrained  ears. 

The  Eye.  —  The  eye  or  organ  of  vision  is  an  almost  spherical  body  which 
fits  into  a  socket  of  bone,  the  orbit.  A  stalklike  structure,  the  optic  nerve, 
connects  the  eye 
with  the  brain. 
Free  movement  is 
obtained  by  means 
of  six  little  muscles 
which  are  attached 
to  the  outer  coat, 
the  eyeball,  and  to 
the  bony  socket 
around  the  eye. 

The  wall  of  the 
eyeball  is  made  up 
of  three  coats.  An 
outer  tough  white 
coat,  of  connective 
tissue,  is  called  the 
sclerotic  coat;  this 
coat  is  lacking  in 
the  exposed  part  of 
the  eyeball,  but  may 
be  seen  by  lifting 
the  eyelid.  Under 
the  sclerotic  coat,  in 
front,  the  eye  bulges 
outward  a  little.  Here  the  outer  coat  is  replaced  by  a  transparent 
tough  layer  called  the  cornea.  A  second  coat,  the  choroid,  is  supplied 
with  blood  vessels  and  cells  which  bear  pigments.  It  is  a  part  of 
this  coat  which  we  see  through  the  cornea  as  the  colored  part  of 
the  eye  (the  iris).  In  the  center  of  the  iris  is  a  small  circular  hole 
(the  pupil).  The  iris  is  under  the  control  of  muscles,  and  may  be  ad- 
justed to  varying  amounts  of  light,  the  hole  becoming  larger  in  dim 
light,  and  smaller  in  bright  light.  The  inmost  layer  of  the  eye  is 
called  the  retina.    This  is,  perhaps,  the  most  delicate  layer  in  the  entire 


LongitudiDal  section  through  the  eye :  Sc,  sclerotic  coat ; 
Ch,  choroid ;  O,  optic  nerve ;  C,  cornea ;  /,  iris ;  Con, 
conjunctiva ;  R,  retina  ;  Y,  yellow  spot ;  L,  lens ;  A,  an- 
terior chamber,  filled  with  aqueous  humor ;  V,  posterior 
chamber,  filled  with  vitreous  humor. 


410    THE  NERVOUS  SYSTEM  AND  ORGANS  OF  SENSE 

body.  Despite  the  fact  that  the  retina  is  less  than  ^V  of  an  inch  in  thick- 
ness, there  are  several  layers  of  cells  in  its  composition.  The  optic  nerve 
enters  the  eye  from  behind  and  spreads  out  over  the  surface  of  the  retina. 
Its  finest  fibers  are  ultimately  connected  with  numerous  elongated  cells 
which  are  stimulated  by  light.  The  retina  is  dark  purple  in  color,  this 
color  being  caused  by  a  layer  of  cells  next  to  the  choroid 
coat.  This  accounts  for  the  black  appearance  of  the 
pupil  of  the  eye,  when  we  look  through  the  pupil  into 
the  darkened  space  within  the  eyeball.  The  retina  acts 
as  the  sensitized  plate  in  the  camera,  for  on  it  are  received 
the  impressions  which  are  transformed  and  sent  to  the 
brain  as  sensations  of  sight.  The  eye,  like  the  camera, 
has  a  lens.  This  lens  is  formed  of  transparent,  elastic 
material.  It  is  found  directly  behind  the  iris  and  is 
attached  to  the  choroid  coat  by  means  of  delicate  liga- 
ments. In  front  of  the  lens  is  a  small  cavity  filled  with 
a  watery  fluid,  the  aqueous  humor,  while  behind  it  is  the 
main  cavity  of  the  eye,  filled  with  a  transparent,  almost 
jellylike,  vitreous  humor.  The  lens  itself  is  elastic.  This 
circumstance  permits  of  a  change  of  form  and,  in  con- 
sequence, a  change  of  focus  upon  the  retina  of  the  lens.  By  means  of 
this  change  in  form,  or  accommodation,  we  are  able  to  distinguish  be- 
tween near  and  distant  objects. 

Defects  in  the  Eye.  —  In  some  eyes,  the  lens  is  in  focus  for  near  objects, 
but  is  not  easily  focused  upon  distant  objects ;   such  an  eye  is  said  to  be 


Diagram  show- 
ing how  the 
lens  changes 
its  form. 


Diagram  to  show  how  an  image  is  formed  in  the  eye:  a,  object;  b,  lens;  c,  image 

upon  retina. 


nearsighted.  Other  eyes  which  do  not  focus  clearly  on  objects  near  at 
hand  are  said  to  be  farsighted.  Still  another  eye  defect  is  astigmatism, 
which  causes  images  of  lines  in  a  certain  direction  to  be  indistinct,  while 


THE  NERVOUS  SYSTEM  AND  ORGANS  OF  SENSE   411 

images  of  lines  transverse  to  the  former  are  distinct.  Many  nervous 
troubles,  especially  headaches,  may  be  due  to  eye  strain.  We  had  better 
have  our  eyes  examined  from  time  to  time,  especially  if  we  have  head- 
aches. 

How  we  See.  —  Suppose  an  object  be  held  in  front  of  the  eye ;  rays 
of  light  pass  from  every  part  of  the  object  and  are  brought  to  a  focus  on 
the  retina  by  means  of  the  transparent  lens.  You  can  form  an  object  in 
the  same  manner  by  using  a  reading  glass,  a  box  with  a  hole  in  one  end,  and 
a  piece  of  white  paper.  Notice  that  the  image  is  inverted.  The  same  is 
true  of  the  image  on  the  retina.  By  means  of  this  image  thrown  on  the 
sensory  layer,  the  rod  and  cone  cells  of  the  retina  are  stimulated  and  the 
image  is  transmitted  to  the  forebrain.  We  must  remember  that  the  optic 
nerve  crosses  under  the  brain  so  that  images  formed  in  the  right  eye  are 
received  by  the  left  half  of  the  forebrain,  and  vice  versa. 

The  Paralyzing  Eflfects  of  Alcohol  on  the  Nervous  System.  —  Alcohol 
has  the  effect  of  temporarily  paralyzing  the  nerve  centers.  The  first  eflPect 
is  that  of  exhilaration.  A  man  may  do  more  work  for  a  time  under  the 
stimulation  of  alcohol.  This  stimulation,  however,  is  of  short  duration 
and  is  invariably  followed  by  a  period  of  depression  and  inertia.  In  this 
latter  state,  a  man  will  do  less  work  than  before.  In  larger  quantities, 
alcohol  has  the  effect  of  completely  paralyzing  the  nerve  centers.  This 
is  seen  in  the  case  of  a  man  "  dead  drunk."  He  falls  in  a  stupor  because 
all  of  the  centers  governing  speech,  sight,  locomotion,  etc.,  have  been 
temporarily  paralyzed.  If  a  man  takes  a  very  large  amount  of  alcohol, 
even  the  nerve  centers  governing  respiration  and  circulation  may  become 
poisoned,  and  the  victim  will  die. 

In  an  article  in  the  Journal  of  Inebriety,  Dr.  J.  W.  Grosvener  of  Buffalo 
says :  "  Alcohol  is  a  paralyzer.  The  truth  of  this  proposition  has  been 
demonstrated  experimentally  scores  of  times  by  world-famed  physiolo- 
gists. Says  Forel :  '  Through  all  parts  of  nervous  activity  from  the  in- 
nervation of  the  muscles  and  the  simplest  sensation  of  the  highest  activity 
of  the  soul  the  paralyzing  effect  of  alcohol  can  be  demonstrated.'  Several 
experimenters  of  undoubted  ability  have  noted  the  paralyzing  effect  of 
alcohol  even  in  small  doses.  By  the  use  of  delicate  instruments  of  precision, 
Ridge  tested  the  effect  of  alcohol  on  the  senses  of  smell,  vision,  and  mus- 
cular sense  of  weight.  He  found  that  two  drams  of  absolute  alcohol 
produced  a  positive  decrease  in  the  sensitiveness  of  the  nerves  of  feeling, 
that  so  small  a  quantity  as  one-half  dram  of  absolute  alcohol  diminished 
the  power  of  vision  and  the  muscular  sense  of  weight.  ICraepelin  and 
Kurz  by  experiment  determined  that  the  acuteness  of  the  special  senses 
of  sight,  hearing,  touch,  taste,  and  smell  was  diminished  by  an  ounce  of 
alcohol,  the  power  of  vision  being  lost  to  one  third  of  its  extent  and  a 
similar  effect  being  produced  on  the  other  special  senses.  Other  investi- 
gators, as  Crothers,  Madden,  Kellogg,  Frey,  Von  Bunge,  have  reached 
like  conclusions." 


412    THE  NERVOUS  SYSTEM  AND  ORGANS  OF  SENSE 

It  is  agreed  by  investigators  that  in  large  or  continued  amounts  alcohol 
has  a  narcotic  effect ;  that  it  first  dulls  or  paralyzes  the  nerve  centers 
which  control  our  judgment,  and  later  acts  upon  the  so-called  motor 
centers,  those  which  control  our  muscular  activities. 

The  reason  then  that  a  man  in  the  first  stages  of  intoxication  talks 
rapidly  and  sometimes  wittily,  is  because  the  centers  of  judgment  are 
paralyzed.  This  frees  the  speech  centers  from  control  exercised  by  our 
judgment,  with  the  resultant  rapid  and  free  flow  of  speech. 

In  small  amounts  alcohol  is  believed  by  some  physiologists  to  have 
always  this  same  narcotic  effect,  while  other  physiologists  think  that 
alcohol  does  stimulate  the  brain  centers,  especially  the  higher  centers, 
to  increased  activity.  Some  scientific  and  professional  men  use  alcohol 
in  small  amounts  for  this  stimulation  and  report  no  seeming  harm  from 
the  indulgence.  Others,  and  by  far  the  larger  number,  agree  that  this 
stimulation  from  alcohol  is  only  apparent  and  that  even  in  the  smallest 
amounts  alcohol  has  a  narcotic  effect. 

The  Relation  of  Alcohol  to  Disease.  —  One  of  the  most  serious  effects 
of  alcohol  is  the  lowered  resistance  of  the  body  to  disease.  It  has  been 
proved  that  a  much  larger  proportion  of  hard  drinkers  die  from  infectious 
or  contagious  diseases  than  from  special  diseased  conditions  due  to  the 
direct  action  of  alcohol  on  the  organs  of  the  body.  This  lowered  resistance 
is  shown  in  increased  liability  to  contract  disease  and  increased  severity 
of  the  disease. 

But  many  cases  of  illness  are  directly  due  to  the  action  of  alcohol  on 
the  tissues.  "  Such  chronic  diseased  conditions  arise  from  the  gradual 
poisoning  of  the  system  by  the  continued  use  of  beverages  containing 
alcohol.  Even  though  we  admit  that  alcohol  in  a  definite  small  amount 
is,  in  some  cases  at  least,  fully  oxidized  in  the  body,  like  the  carbohy- 
drates, and  so  supplies  energy  as  food,  we  must  never  forget  that  different 
constitutions  may  be  differently  affected,  and  conditions  as  to  climate, 
temperament,  and  habits  of  life  may  cause  variations  in  its  influence  upon 
health  and  character.  We  can  never  know  perfectly  the  nature  of  all  the 
innumerable  strains  of  hereditary  tendency  which  unite  to  make  an 
individual  what  he  is.  Some  one  of  these  may  have  impressed  upon  the 
nerve  cells  an  instability,  a  weakness,  a  peculiar  susceptibility  to  the  in- 
fluence of  alcohol,  so  that  the  first  taste  may  arouse  the  insatiable  craving 
which  leads  to  dipsomania.  In  another  case,  the  inherited  weakness  may 
render  the  child  of  an  inebriate  an  epileptic,  an  imbecile,  or  a  consumptive. 
We  can  never  foresee  just  how  the  transmitted  nervous  weakness  will 
manifest  itself,  but  as  a  rule  the  descendants  of  those  whose  systems  are 
poisoned  by  alcohol  are  enfeebled  in  body  or  mind  or  both. 

**  But  suppose  a  man  to  have  derived  from  his  ancestors  a  sound  con- 
stitution and  to  have  become  addicted  to  the  moderate  use  of  alcohol ; 
the  insidious  nature  of  the  dangerous  substance  may  gradually  lead  him 
to  consume,  insensibly  perhaps,  only  a  little  more  than  the  cells  can  oxidize. 


THE  NERVOUS  SYSTEM  AND  ORGANS  OF  SENSE    413 

Without  realizing  it,  he  may  slowly  poison  his  system.  The  primary  effect 
is  upon  the  brain;  there  is  congestion  and  overexcitement  of  the  nerve 
cells  there  —  conditions  which  gradually  extend  to  the  nerve  cells  of  the 
spinal  cord ;  inflammation  sets  in,  and  there  follows  fibrous  degeneration 
of  the  tissues,  substituting  an  inferior  form  for  the  specialized  tissues  which 
do  the  work  of  the  organs  in  various  parts  of  the  body.  Paralysis  may 
result,  or  epilepsy,  or  dyspepsia  from  lack  of  the  due  amount  of  nervous 
influence  upon  the  digestive  organs,  or  any  one  of  a  thousand  forms  of 
disorder,  some  of  which  have  been  mentioned  in  preceding  chapters. 
Though  a  man  may  never  drink  to  intoxication,  and  never  realize  that  he 
is  using  alcohol  to  excess,  he  may  nevertheless  become  seriously  diseased 
in  consequence  of  his  moderate  indulgence,  or  what  he  believes  to  be  such, 
while  wondering  why  he  is  not  well  and  strong.  Still  less  does  he  con- 
sider the  legacy  of  evil  which  he  may  be  laying  up  for  his  children."  — 
Macy,  Physiology.      (See  Laboratory  Manual,  Prob.  LVI.) 

Effect  of  Alcohol  on  Ability  to  do  Work.  —  In  Physiological  Aspects 
of  the  Liquor  Problem,  Professor  Hodge  of  Clark  University  describes  many 
of  his  own  experiments  showing  the  effect  of  alcohol  on  animals.  He 
trained  four  selected  puppies  to  recover  a  ball  thrown  across  a  gymnasium. 
To  two  of  the  dogs  he  gave  food  mixed  with  dietetic  doses  of  alcohol,  while 
the  others  were  fed  normally.  The  ball  was  thrown  100  feet  as  rapidly  as 
recovered.  This  was  repeated  100  times  each  day  for  fourteen  successive 
days.  Out  of  1400  times  the  dogs  to  which  alcohol  had  been  given  brought 
back  the  ball  only  478  times,  while  the  others  secured  it  922  times. 

Dr.  Parkes  experimented  with  two  gangs  of  men,  selected  to  be  as 
nearly  similar  as  possible,  in  mowing.  He  found  that  with  one  gang 
abstaining  from  alcoholic  drinks  and  the  other  not,  the  abstaining 
gang  could  accomplish  more.  On  transposing  the  gangs  the  same  results 
were  repeatedly  obtained.  Similar  results  were  obtained  by  Professor 
Aschaffenburg  of  Heidelberg  University,  who  found  experimentally  that 
men  "  were  able  to  do  15  per  cent  less  work  after  taking  alcohol."  Profes- 
sor Abel  of  Johrs  Hopkins  University  says,  "  Both  science  and  the  ex- 
perience of  life  have  exploded  the  pernicious  theory  that  alcohol  gives  any 
persistent  increase  of  muscular  power." 

The  Effect  of  Alcohol  upon  Intellectual  Ability.  —  With  regard  to  the 
supposed  quickening  of  the  mental  processes  Horsley  and  Sturge,  in  their 
recent  book.  Alcohol  and  the  Human  Body,  say :  "  Kraepelin  found 
that  the  simple  reaction  period,  by  which  is  meant  the  time  occupied  in 
making  a  mere  response  to  a  signal,  as,  for  instance,  to  the  sudden  ap- 
pearance of  a  flag,  was,  after  the  ingestion  of  a  small  quantity  of  alcohol 
i\  to  i  ounce),  slightly  accelerated;  that  there  was,  in  fact,  a  slight 
shortening  of  the  time,  as  though  the  brain  were  enabled  to  operate  more 
quickly  than  before.  But  he  found  that  after  a  few  minutes,  in  most  cases, 
a  slowing  of  mental  action  began,  becoming  more  and  more  marked,  and 
enduring  as  long  as  the  alcohol  was  in  active  operation  in  the  body,  i.e. 


414    THE  NERVOUS  SYSTEM  AND  ORGANS  OF  SENSE 

four  to  five  hours.  .  .  .  Kraepelin  found  that  it  was  only  more  or  less 
automatic  work,  such  as  reading  aloud,  which  was  quickened  by  alcohol, 
though  even  this  was  rendered  less  trustworthy  and  accurate."  Again: 
"  Kraepelin  had  always  shared  the  popular  belief  that  a  small  quantity 
of  alcohol  (one  to  two  teaspoonfuls)  had  an  accelerating  effect  on  the 
activity  of  his  mind,  enabling  him  to  perform  test  operations,  as  the  adding 
and  subtracting  and  learning  of  figures  more  quickly.  But  when  he  came 
to  measure  with  his  instruments  the  exact  period  and  time  occupied,  he 
found,  to  his  astonishment,  that  he  had  accomplished  these  mental  opera- 
tions, not  more,  but  less,  quickly  than  before.  .  .  .  Numerous  further 
experiments  were  carried  out  in  order  to  test  this  matter,  and  these  proved 
that  alcohol  lengthens  the  time  taken  to  perform  complex  mental  processes^ 
while  by  a  singular  illusion  the  person  experimented  upon  imagines  that 
his  psychical  actions  are  rendered  more  rapid." 

Professor  Woodhead  says,  "  After  careful  examination  of  the  whole 
question,  physiologists  —  and  among  physiologists  I  include  those  who 
maintain  alcohol  may  be  useful,  as  well  as  those  who  hold  that  it  is  harm- 
ful —  have  come  to  the  conclusion  that  the  principal  action  of  alcohol  is 
to  blunt  sensation,  and  to  remove  what  we  may  call  the  power  of  inhibition 
by  blunting  the  higher  centers  of  the  brain." 

Professor  David  Starr  Jordan  in  the  Popular  Science  Monthly,  Febru- 
ary, 1898,  said:  "  The  healthy  mind  stands  in  clear  and  normal  relations 
with  nature.  It  feels  pain  as  pain.  It  feels  action  as  pleasure.  The 
drug  which  conceals  pain  or  gives  false  pleasure  when  pleasure  does  not 
exist  forces  a  lie  upon  the  nervous  system.  The  drug  which  disposes  to 
reverie  rather  than  to  work,  which  makes  us  feel  well  when  we  are  not 
well,  destroys  the  sanity  of  life.  All  stimulants,  narcotics,  tonics,  which 
affect  the  nervous  system  in  whatever  way,  reduce  the  truthfulness  of  sen- 
sation, thought,  and  action.  Toward  insanity  all  such  influences  lead; 
and  their  effect,  slight  though  it  be,  is  of  the  same  nature  as  mania.  The 
man  who  would  see  clearly,  think  truthfully,  and  act  effectively  must  avoid 
them  all.  Emergency  aside,  he  cannot  safely  force  upon  his  nervous  sys- 
tem even  the  smallest  falsehood." 

Dr.  Hammond  said :  "  The  more  piu-ely  intellectual  qualities  of  the 
mind  rarely  escape  being  involved  in  the  general  distiu-bance  [caused  by 
alcohol].  The  power  of  application,  of  appreciating  the  bearing  of  facts, 
of  drawing  distinctions,  of  exercising  the  judgment  aright,  and  even  of 
comprehension,  are  all  more  or  less  impaired.  The  memory  is  among 
the  first  faculties  to  suffer.  .  .  .  The  will  is  always  lessened  in  force  and 
activity.  The  ability  to  determine  between  two  or  more  alternatives,  to 
resolve  to  act  when  action  is  necessary,  no  longer  exists  in  full  power,  and 
the  individual  becomes  vacillating,  uncertain,  the  prey  to  his  various 
passions,  and  to  the  influence  of  vicious  counsels." 

"  Finally  we  have  still  to  declare  that  alcohol  hinders  the  action  of  the 
highest  mental  faculties.    A  remark  made  by  Helmholtz  at  the  celebration 


THE  NERVOUS  SYSTEM  AND  ORGANS  OF  SENSE    415 

of  his  seventieth  birthday  is  very  interesting  in  this  connection.  He 
spoke  of  the  ideas  flashing  up  from  the  depths  of  the  unknown  soul,  that 
lies  at  the  foundation  of  every  truly  creative  intellectual  production,  and 
closed  his  account  of  their  origin  with  these  words :  '  The  smallest  quan- 
tity of  an  alcoholic  beverage  seemed  to  frighten  these  ideas  away.'  "  — 
Dr.  G.  Sims  Woodhead,  Professor  of  Pathology,  Cambridge  University, 
England. 

"  Some  people  imagine  that  after  the  use  of  alcohol  they  can  do  things 
more  quickly,  that  they  are  brisker  and  sharper,  but  exact  measurement 
shows  that  they  are  slower  and  less  accurate.  Men  believe  that  they  are 
wiser  and  brighter,  but  their  sayings  are  more  automatic  and  apt  to  be 
profane.  To  quote  Dr.  Lauder  Brunton,  of  Oxford  University,  England, 
'  It  produces  progressive  paralysis  of  the  judgment,''  and  this  begins  with 
the  first  glass.  Men  say  and  do,  even  after  a  single  glass  of  drink,  what 
they  would  not  say  or  do  without  it,  and  therefore  it  clearly  affects  the 
brain  and  diminishes  self-control."  — Adolph  Fick,  Professor  of  Physiology, 
Wiirzburg,  Germany. 

Professor  Von  Bunge  ( Textbook  of  Physiological  and  Pathological  Chem- 
istry) of  Switzerland  says  that :  "  The  stimulating  action  which  alcohol 
appears  to  exert  on  the  brain  functions  is  only  a  paralytic  action.  The 
cerebral  functions  which  are  first  interfered  with  are  the  power  of  clear  judg- 
ment and  reason.  No  man  ever  became  witty  by  aid  of  spirituous  drinks. 
The  lively  gesticulations  and  useless  exertions  of  intoxicated  people  are 
due  to  paralysis,  —  the  restraining  influences,  which  prevent  a  sober  man 
from  uselessly  expending  his  strength,  being  removed." 

"  The  capital  argument  against  alcohol,  that  which  must  eventually 
condemn  its  use,  is  this,  that  it  takes  away  all  the  reserved  control,  the  power 
of  mastership,  and  therefore  offends  against  the  splendid  pride  in  himself 
or  herself,  which  is  fundamental  in  every  man  or  woman  worth  anything.''  -=- 
—  Dr.  John  Johnson,  quoting  Walt  Whitman. 

The  Drink  Habit.  —  The  harmful  effects  of  alcohol  (aside  from 
the  purely  physiological  effect  upon  the  tissues  and  organs  of  the 
body)  are  most  terribly  seen  in  the  formation  of  the  alcohol  habit. 
The  first  effect  of  drinking  alcoholic  liquors  is  that  of  exhilaration. 
After  the  feeling  of  exhilaration  is  gone,  for  this  is  a  temporary 
state,  the  subject  feels  depressed  and  less  able  to  work  than  before 
he  took  the  drink.  To  overcome  this  feeling,  he  takes  another 
drink.  The  result  is  that  before  long  he  finds  a  habit  formed  from 
which  he  cannot  escape.  With  body  and  mind  weakened,  he 
attempts  to  break  off  the  habit.  But  meanwhile  his  will,  too, 
has  suffered  from  overindulgence.  He  has  become  a  victim  of  the 
drink  habit ! 


416    THE  NERVOUS  SYSTEM  AND  ORGANS  OF  SENSE 

Self-indulgence,  be  it  in  gratification  of  such  a  simple  desire  as 
that  for  candy  or  the  more  harmful  indulgence  in  tobacco  or  al- 
coholic beverages,  is  dangerous  —  not  only  in  its  immediate  effects 
on  the  tissues  and  organs,  but  in  its  more  far-reaching  effects  on 
habit  formation. 

"  S§lf-control  versus  Appetite.  —  Man  is  a  bundle  of  appetites.  Every 
organ,  every  cell  even,  craves  its  appropriate  stimulus.  Animals  under 
natural  conditions  gratify  the  appetites  as  they  arise  only  to  that  extent 
which  is  healthful  for  the  whole  body.  Man  alone,  whose  highly  developed 
brain  is  overlord  to  the  rest  of  his  system,  permits  an  unwholesome  indul- 
gence of  appetite  to  interfere  with  this  general  well-being.  Alcohol,  opium, 
and  their  like  are  far  from  being  the  only  substances  whose  excessive  use 
injures  the  organism  and  degrades  character.  Children  are  often  allowed 
to  indulge  a  natural  fondness  for  sweets  to  an  extent  which  is  ruinous  to 
digestion ;  for  sugar,  which  is  a  useful  and  necessary  food  in  suitable  quan- 
tities, becomes  in  larger  ones  a  poison  to  the  system.  Boys  pampered 
with  dainties  from  infancy  logically  infer  that  a  fancy  for  cigars  or  beer 
may  be  similarly  gratified.  Appetite  for  even  the  most  wholesome  food 
may  be  in  excess  of  bodily  needs,  and  the  practice  of  gluttony  is  certain 
to  derange  nutrition. 

"  A  child  should  be  early  taught  that  because  he  '  likes  '  a  certain  arti- 
cle of  food  he  should  not  therefore  continue  to  eat  it  after  natural  hunger 
is  satisfied,  or  at  times  when  he  does  not  need  food ;  while  to  persist  in 
eating  or  drinking  that  which  experience,  or  the  advice  of  those  competent 
to  judge,  has  taught  him  to  be  harmful,  should  be  regarded  as  unworthy 
a  rational  being."  —  Macy,  Physiology. 

The  Moral,  Social,  and  Economic  Effect  of  Alcoholic  Poisoning. — ■ 
In  the  struggle  for  existence,  it  is  evident  that  the  man  whose  in- 
tellect is  the  quickest  and  keenest,  whose  judgment  is  most  sound, 
is  the  man  who  is  most  likely  to  succeed.  The  paralyzing  effect 
of  alcohol  upon  the  nerve  centers  must  place  the  drinker  at  a  dis- 
advantage. In  a  hundred  ways,  the  drinker  sooner  or  later  feels 
the  handicap  that  the  habit  of  drink  has  imposed  upon  him.  Many 
corporations,  notably  several  of  our  greatest  railroads  (the  New 
York  Central  Railroad  among  them),  refuse  to  employ  any  but 
abstainers  in  positions  of  trust.  Few  persons  know  the  num- 
ber of  railway  accidents  due  to  the  uncertain  eye  of  some  engineer 
who  mistook  his  signal,  or  the  hazy  inactivity  of  the  brain  of  some 
train  dispatcher  who,  because  of  drink,  forgot  to  send  the  tele- 
gram that  was  to  hold  the  train  from  wreck. 


THE  NERVOUS  SYSTEM  AND  ORGANS  OF  SENSE   417 

In  business  and  in  the  professions,  the  story  is  the  same.  The 
abstainer  wins  out  over  the  drinking  man. 

Not  alone  in  activities  of  life,  hut  in  the  length  of  life,  has  the 
abstainer  the  advantage.  Figures  presented  by  Ufe  insurance  com- 
panies show  that  the  nondrinkers  have  a  considerably  greater 
chance  of  long  life  than  do  drinking  men.  So  decided  are  these 
figures  that  several  companies  have  lower  premiums  for  the  non- 
drinkers  than  for  the  drinkers  who  insure  with  them. 

"  Other  Narcotics  in  Common  Use.  —  Narcotics  are  very  widely  used 
by  the  human  family  for  the  relief  which  they  g^ve  from  pain  or  fatig^ue, 
or  for  the  direct  pleasurable  sensations  which  they  impart.  All  are  deadly 
poisons  when  taken  in  sufficient  quantities.  Those  most  common  (after 
alcohol)  are  tobacco  and  opium. 

"  It  has  already  been  shown  that  tobacco  may  affect  unfavorably  many 
parts  of  the  system,  and  is  especially  injurious  to  the  young.  It  stimu- 
lates in  small  quantities  and  narcotizes  in  larger  ones,  working  its  effects 
directly  upon  the  nervous  system.  Nicotine,  the  powerful  poison  found 
in  tobacco,  affects  the  nerve  cells,  injures  the  brain,  and  leads  especially 
to  weakness  of  the  heart  by  interfering  with  its  supply  of  nervous  force. 
Many  cases  of  cancer  of  mouth  and  throat  are  believed  to  have  resulted 
from  tobacco  smoking. 

"  Opium,  for  its  benumbing  influence  upon  the  nerves,  is  used  by  large 
numbers  of  persons,  especially  in  Oriental  lands.  Its  continued  use  de- 
ranges all  the  digestive  processes,  disorders  the  brain,  and  weakens  and 
degrades  the  character.  Like  alcohol,  it  produces  an  intolerable  craving 
for  itself,  and  the  strongest  minds  are  not  proof  against  the  deadly  appetite." 

Heferencb  Rbadixq 

ELEMENTARY 

Sharpe,  A  Laboratory  Manual  for  the  Solution  of  Problems  in  Biology.    American 

Book  Company. 
Davison,  The  Human  Body  and  HeaJth.     American  Book  Company. 
The  Gulick  Hygiene  Series,  Emergencies,  Good  Health,  The  Body  at  Work,  Control 

of  Body  and  Mind.     Ginn  and  Company. 
Moore,  Physiology  of  Man  and  other  Animals.     Henry  Holt  and  Company. 
Ritchie,  Human  Physiology.     Worid  Book  Company. 

ADVANCED 

Hough  and  Sedgwick,  The  Human  Mechanism.     Ginn  and  Company.     See  also 
references  given  at  the  end  of  Chapter  XXIII. 


HUNT.  ES.  BIO.  —  27 


XXIX.    HEALTH  AND   DISEASE— A  CHAPTER  ON  CIVIC 

BIOLOGY 

Problem  LVI,  A  study  of  personal  and  civic  hygiene,  {Laho' 
ratory  Manual,  Proh.  L  J 'I.) 

Health  and  Disease.  —  In  previous  chapters  we  have  consid- 
ered the  body  as  a  machine  more  deUcate  in  its  organization  than 
the  best-built  mechanism  made  by  man.  In  a  state  of  health  this 
human  machine  is  in  a  good  condition;  disease  is  a  condition  in 
which  some  part  of  the  body  is  out  of  order,  thus  interfering  with 
the  smooth  running  of  the  mechanism. 

Personal  Hygiene.  —  It  is  the  purpose  of  the  study  of  hygiene 
to  show  us  how  to  live  so  as  to  keep  the  body  in  a  healthy  state. 
Hygiene  not  only  prescribes  certain  laws  for  the  care  of  the  various 
parts  of  the  body,  — skin,  teeth,  the  food  tube  or  the  sense  organs, 
—  but  it  also  shows  us  how  to  avoid  disease.  The  foundation  of 
health  later  in  life  is  laid  down  at  the  time  we  are  in  school;  for 
that  reason,  if  for  no  other,  a  knowledge  of  the  laws  of  hygienic 
living  are  necessary  for  all  school  children.  Unlike  the  lower 
animals,  we  can  change  or  modify  our  immediate  surroundings  so 
as  to  make  them  better  and  more  hygienic  places  to  live  in.  Hy- 
gienic living  in  our  home  must  go  hand  in  hand  with  sanitary 
conditions  around  us.  It  is  the  purpose  of  this  chapter  to  show 
how  we  do  our  share  to  cooperate  with  those  in  charge  of  the 
public  health  in  our  towns  and  cities. 

Some  Methods  of  Prevention  of  Disease.  —  The  proverb  ''  An 
ounce  of  prevention  is  worth  a  pound  of  cure  "  has  much  truth  in 
it.  Disease  is  largely  preventable.  Fresh  air,  the  needed  amount 
of  sleep,  moderate  exercise,  and  pure  food  and  water  are  essentials 
in  hygienic  living  and  in  escape  from  disease. 

Pure  Air  Needed.  —  What  do  we  mean  by  fresh  air,  and  why  do 
we  need  it?  We  have  already  seen  that  oxidation  takes  place 
within  the  body,  and  that  air  containing  as  little  as  2  parts  of 
respired  carbon  dioxide  to  10,000  parts  of  air  is  bad  for  breathing. 

418 


HEALTH  AND  DISEASE 


419 


In  addition  to  the  carbon  dioxide,  water  and  heat  are  given  off  as 
well  as  a  very  small  amount  of  organic  material  of  a  poisonous 
nature.  It  is  the  presence  of  this  material  that  gives  rise  to  the 
odor  noticeable  in  a  close  room.  But  other  organic  material  is 
found  in  air.  Dust  from  the  street  contains  bacteria  of  all 
kinds,  some  of  wliich  may  be  disease-producing.  Thus  may  be 
spread  bacteria  from  the  respiratory  tracts  of  people  who  have 
colds,  pneumonia,  diphtheria,  or  tuberculosis.     Much  dust  is  dried 


Two  cultures  (A)  were  exposed  to  the  air  of  a  dirty  street  in  the  crowded  part  of 
Manhattan.  (B)  was  exposed  to  the  air  of  a  well-cleaned  and  watered  street  in 
the  uptown  residence  portion.  Which  culture  has  the  most  colonies  of  bacteria? 
How  do  you  account  for  this  ? 


excreta  of  animals.  Soft-coal  smoke  does  its  share  to  add  to  the 
impurities  of  the  air,  while  sewer  gas  and  illuminating  gas  are 
frequently  found  in  sufficient  quantities  to  poison  people.  Pure 
air  is,  as  can  be  seen,  almost  an  impossibility  in  a  great  city 

How  to  get  Fresh  Air.  —  As  we  know,  green  plants  give  off  in 
the  sunlight  considerable  more  oxygen  than  they  use,  and  they 
use  up  carbon  dioxide.  The  air  in  the  country  is  naturally  purer 
than  in  the  city,  as  smoke  and  bacteria  are  not  so  prevalent  there, 
and  the  plants  in  abundance  give  off  oxygen.  In  the  city  the 
night  air  is  purer  than  day  air,  because  the  factories  have  stopped 
work,  the  dust  has  settled,  and  fewer  people  are  on  the  streets. 
The  old  myth  of  "  night  air  "  being  injurious  has  long  since  been 
exploded,  and  thousands  of  people  of  dehcate  health,  especially 


420 


HEALTH  AND  DISEASE 


those  who  have  weak  throat  or  lungs,  are  regaining  health  by 
sleeping  out  of  doors  or  with  the  windows  wide  open.  The  only 
essential  in  sleeping  out  of  doors  or  in  a  room  with  a  low  tem- 
perature is  that  the  body  be  kept  warm  and  the  head  be  protected 
from  strong  drafts  by  a  nightcap  or  hood.  Proper  ventilation  at 
all  times  is  one  of  the  greatest  factors  in  good  health. 

Change  of  Air. — Persons  in  poor  health,  especially  those  having 
tuberculosis,  are  often  cured  by  a  change  of  air.  This  is  not 
always  so  much  due  to  the  composition  of  the  air  as  to  change  of 
occupation,  rest,  and  good  food.  Mountain  air  is  dry,  and  rela- 
tively free  from  dust  and  bacteria,  and  often  helps  a  person 
having  tuberculosis.  Air  at  the  seaside  is  beneficial  for  some 
forms  of  disease,  especially  hay  fever  and  bone  tuberculosis. 
Many  sanitariums  Jiave  been  established  for  this  latter  disease 
near  the  ocean,  and  thousands  of  lives  are  being  annually  saved 
in  this  way. 

The  Relation  of  Pure  Food  and  Pure  Water  to  Health.  —  Thanks 
to  the  care  of  state  and  city  governments  there  is  little  need  now- 
adays for  the  health  of  any  in- 
dividual to  suffer  from  impure 
food  or  water.  But  that  people 
do  become  sick  and  die  from 
such  causes  every  day  is  well 
known,  as  is  shown  by  the 
many  cases  of  typhoid  fever, 
summer  complaint,  and  pto- 
maine poisoning  of  various 
sorts.  Our  milk  may  have 
been  watered  or  sent  in  cans 
washed  with  water  containing 
tj^hoid  germs,  we  may  eat 
oysters  bred  in  contaminated 
localities,  we  may  have  re- 
ceived and  eaten  fruits  or 
vegetables  sprinl<;led  with  water  containing  the  germs.  Our  laws, 
however  good,  cannot  cope  with  human  carelessness.  Not  only 
should  we  as  individuals  demand  from  the  source  of  supply  pure 
food  and  water,  but  we  should  do  our  share  at  home  to  keep  them 


Tracks  of  germs  left  by  a  fly  crawling  on  a 
culture  in  a  dish. 


HEALTH  AND  DISEASE  421 

pure.  Flies  and  other  insects  should  be  prevented  from  reaching 
food.  Vegetables  and  fruits  must  not  be  eaten  in  an  unripe  or 
half-rotted  condition,  nor  should  the  latter  be  canned  or  preserved. 
All  raw  fruits  or  vegetables  that  are  not  protected  by  the  skin 
should  be  washed  before  eating.  In  general,  foods  may  be  made 
safe  to  eat  by  cooking  long  enough  to  kill  the  germs.  Milk  to  be 
rendered  absolutely  safe  should  be  pasteurized  (so  called  after 
Louis  Pasteur,  the  inventor  of  the  process),  that  is,  treated  to  160° 
Fahrenheit  for  20  minutes.  Ptomaine  poisoning  is  often  caused 
by  the  growth  of  bacteria  in  canned  material.  These  bacteria 
were  not  all  killed  by  the  cooking,  grew,  and  gave  off  the  poison 
or  ptomaines.  Such  foods  are  dangerous,  for  cooking  does  not 
destroy  the  poison.  Meats  which  have  been  hung  so  long  as  to 
have  an  odor,  and  cold  storage  meats  that  appear  to  be  decayed, 
should  be  avoided. 

Relation  of  Proper  Exercise  and  SuflScient  Sleep  to  Health.  — 
We  are  all  aware  that  exercise  in  moderation  has  a  beneficial  effect 
upon  the  human  organism.  The  pale  face,  drooping  shoulders, 
and  narrow  chest  of  the  boy  or  girl  who  takes  no  regular  exercise 
is  too  well  known.  Exercise,  besides  giving  direct  use  of  the  mus- 
cles, increases  the  work  of  the  heart  and  lungs,  causing  deeper 
breathing  and  giving  the  heart  muscles  increased  work ;  it  liberates 
heat  and  carbon  dioxide  from  the  tissues  where  the  work  is  taking 
place,  thus  increasing  the  respiration  of  the  tissues  themselves, 
and  aids  mechanically  in  the  removal  of  wastes  from  tissues.  It 
is  well  known  that  exercise,  when  taken  some  little  time  after  eating, 
has  a  very  beneficial  effect  upon  digestion.  Exercise  and  games, 
especially  if  a  change  of  occupation,  are  of  immense  importance  to 
the  nervous  system  as  a  means  of  rest.  The  increasing  number  of 
playgrounds  in  this  country  is  due  to  this  acknowledged  need  of 
exercise,  especially  for  growing  children. 

Proper  exercise  should  be  moderate  and  varied.  Walking  in 
itself  is  a  valuable  means  of  exercising  certain  muscles,  so  is  bicy- 
cling, but  neither  is  ideal  as  the  only  form  to  be  used.  Vary  your 
exercise  so  as  to  bring  different  muscles  into  play,  take  exercise 
that  will  allow  free  breathing  out  of  doors  if  possible,  and  the 
natural  fatigue  which  follows  will  lead  us  to  take  the  rest  and  sleep 
that  every  normal  body  requires. 


4^  HEALTH  AND  DISEASE 

Sleep  is  one  way  in  which  all  cells  in  the  body  and  particularly 
those  of  the  nervous  system  get  their  rest.  The  nervous  system, 
by  far  the  most  delicate  and  hardest  worked  set  of  tissues  in  the 
body,  needs  rest  more  than  do  other  tissues,  for  its  work  directing 
the  body  only  ends  with  sleep  or  unconsciousness.  The  afternoon 
nap,  snatched  by  the  brain  worker,  gives  him  renewed  energy  for 
his  evening's  work.  It  is  not  hard  application  to  a  task  that 
wearies  the  brain;   it  is  continuous  work  without  rest. 

Efifect  of  Alcohol  on  the  Ability  to  Resist  Disease.  —  Among 
certain  classes  of  people  the  belief  exists  that  alcohol  in  the  form  of 
brandy  or  some  other  drink  or  in  patent  medicines,  malt  tonics, 
and  the  like  is  of  great  importance  in  building  up  the  body  so  as 
to  resist  disease  or  to  cure  it  after  disease  has  attacked  it.  Nothing 
is  further  from  the  truth.  In  experiments  on  over  three  hundred 
animals,  including  dogs,  rabbits,  guinea  pigs,  fowls,  and  pigeons, 
Laitenen  of  the  University  of  Helsingsfors  and  Professor  Frankel 
of  Halle  found  that  alcohol  without  exception  made  these  animals 
more  susceptible  to  disease  than  were  the  controls. 

Use  of  Alcohol  in  the  Treatment  of  Disease.  —  In  the  Lon- 
don Temperance  Hospital  alcohol  was  prescribed  seventy-five 
times  in  thirty-three  years.  The  death  rate  in  this  hospital  has 
been  lower  than  that  of  most  general  hospitals.  Sir  William 
Collins,  after  serving  nineteen  years  as  surgeon  in  this  hospital, 
said :  — 

'*  In  my  experience,  speaking  as  a  surgeon,  the  use  of  alcohol  is  not 
essential  for  successful  surgery.  ...  At  the  London  Temperance  Hos- 
pital, where  alcohol  is  very  rarely  prescribed,  the  mortality  in  amputation 
cases  and  in  operation  cases  generally  is  remarkably  low.  Total  abstainers 
are  better  subjects  for  operation,  and  recover  more  rapidly  from  accidents, 
than  those  who  habitually  take  stimulants." 

Dr.  MacNichoU  says :  *'  During  a  period  of  ten  years  the  Chicago 
hospitals  in  which  alcohol  was  employed  in  pneumonia  showed  a  death 
rate  of  twenty-eight  to  thirty-eight  per  cent.  Non-alcoholic  medication 
during  the  same  period  at  the  Mercy  Hospital  showed  a  death  rate  in 
pneumonia  of  less  than  twelve  per  cent.  .  .  .  The  mortality  in  our  hos- 
pitals bears  a  very  close  relation  to  the  per  capita  of  alcohol  prescribed.  In 
the  Fordham  Hospital,  where  seventy-two  cents  per  capita  of  alcohol  is 
prescribed,  one  out  of  every  eight  patients  who  enter  for  treatment  dies. 
In  the  German  Hospital,  Philadelphia,  where  forty-three  cents  per  capita 
of  alcohol  is  prescribed,  one  of  every  sixteen  patients  die.     In  the  Red 


HEALTH  AND  DISEASE  423 

Cross  Hospital,  New  York  City,  where  no  alcohol  is  prescribed,  one  out 
of  one  hundred  and  four  patients  die." 

Dr.  S.  A.  Knopf  says:  "Alcohol  does  not  cure  tuberculosis  I  Used 
in  excess  and  injudiciously  administered,  it  surely  retards  recovery." 

Dr.  Legrain,  senior  physician  to  the  asylum  Ville  Evrard,  Paris,  de- 
clares :  "  The  systematic  treatment  of  chronic  tuberculosis  by  alcohol 
is  apparently  a  physiological  absurdity." 

Professor  Guttstadt  of  Berlin  publishes  statistics  showing  that 
in  Prussia  of  every  1000  deaths  of  men  over  twenty-five  years,  161 
are  from  tuberculosis.  Of  every  1000  deaths  among  bartenders, 
556  are  from  tuberculosis ;  among  brewery  employees,  345 ;  school- 
teachers, 143  ;  physicians,  113 ;  clergy,  76.  The  55th  annual  report 
of  the  British  Registrar  General  gives  the  average  death  rate  of 
England  as  13  per  thousand,  but  among  brewers  it  is  41  per  thou- 
sand, only  four  occupations  showing  a  higher  rate. 

In  a  paper  read  at  the  International  Congress  on  Tuberculosis,  in  New 
York,  19(X),  Dr.  Crothers  remarked  that  alcohol  as  a  remedy  or  a  pre- 
ventive medicine  in  the  treatment  of  tuberculosis  is  a  most  dangerous 
drug,  and  that  all  preparations  of  sirups  containing  spirits  increase,  rather 
than  diminish,  the  disease. 

Dr.  Kellogg  says :  "  The  grave  significance  of  the  effects  of  alcohol 
upon  living  cells  can  be  fully  appreciated  only  when  we  keep  in  mind  the 
fact  that  phagocytosis  is  the  chief  means  of  bodily  defense  against 
bacterial  disease.  It  is  only  through  leucocytosis  —  the  migration  of 
leucocytes,  and  their  activity  in  attacking  and  destroying  bacteria  — 
that  recovery  from  any  infectious  disease  is  possible.  The  paralyzing 
influence  of  alcohol  upon  the  white  cells  of  the  blood  —  a  fact  which  is 
attested  by  all  investigators  —  is  alone  suflBcient  to  condemn  the 
use  of  this  drug  in  acute  or  chronic  infections  of  any  sort." 

Experience  of  Insurance  Companies.  —  The  United  Kingdom 
Temperance  and  General  Provident  Institution  of  London  insures 
in  two  departments,  a  general  section  and  one  for  total  abstainers. 
During  the  sixty  years  from  1841  to  1901  there  were  31,776  whole- 
life  policies  in  the  general  or  nonabstaining  section.  These  passed 
through  446,943  years  of  life,  and  there  were  8947  deaths.  In 
the  abstaining  section  there  were  29,094  whole-life  policies,  passing 
through  398,010  years  of  life,  with  5124  deaths.  If  the  death  rate 
in  the  abstaining  section  had  equaled  that  in  the  general  section, 
there  would  have  been  6959  deaths  instead  of  5124,  or  the  mortality 


424  HEALTH  AND  DISEASE 

averaged  36  per  cent  higher  in  the  nonabstaining  section  than  in 
the  abstaining  section. 

In  his  article  published  in  the  book  by  Horsley  and  Sturge, 
Dr.  Arthur  Newsholme  says :  — 

,"  Out  of  every  100,000  starting  at  the  age  of  twenty,  among  the  ab- 
stainers 53,044  reach  the  age  of  seventy,  while  only  42,109  reach  this  age 
in  the  general  experience  of  a  large  number  of  life  offices  of  Great 
Britain." 

Of  100,000  total  abstainers  starting  at  twenty 
53,044  reach  70  years;  46,956  die  before  70  years;  and 
of  100,000  moderate  drinkers  starting  at  twenty 
42,109  reach  70  years;  57,891  die  before  70  years 

In  the  Scottish  Temperance  Life  Assurance  Society,'  in  the  twenty 
years  ending  1897,  the  deaths  amounted  to  69  per  cent  of  the  ex- 
pected mortality  in  the  general  section,  while  in  the  total  abstainers' 
section  they  amounted  to  only  47  per  cent  of  the  expected  number. 
The  niunber  of  deaths  in  the  general  section  of  the  Sceptre  Life 
Association,  England,  was  80.34  per  cent  of  the  expectation  in  the 
fifteen  years  ending  1808,  but  in  the  total  abstainers'  section  it  was 
only  56.37  per  cent  of  the  expected  mortality. 

In  considering  the  statistics  of  the  insurance  companies,  it  is 
well  to  remember  that  those  insured  in  the  general  sections  were 
picked  men  as  well  as  those  in  the  total  abstainers'  sections. 

In  discussing  the  experience  of  fraternal  societies,  Dr.  News- 
holme  gives  the  following  statistics  from  the  report  of  the  Public 
Actuary  of  South  AustraUa :  — 

Average  Mor-        Average 
TALiTT  Per         Sickness  in 
Cent  Weeks 

Abstainers'  Societies 0.689  1.248 

Nonabstainers'  Societies 1.381  2.317 

Mortality  Peb  Average  Weeks  of 

Cent  op  Sick  Sickness  per  Each 

Members  Member  Sick 

Abstainers*  Societies       ......        3.557  6.45 

Nonabstainers'  Societies 6.532  10.91 

Attention  should  be  called  to  the  fact  that  the  nonabstain- 
ers' societies  have  many  members  who  are  total  abstainers,  but, 
unlike   the   abstainers'  societies,  they  do  not  refuse  to  admit 


HEALTH  AND  DISEASE  425 

nonabstainers.  The  number  of  weeks  of  sickness  in  the  table 
refers  to  the  average  number  of  weeks  for  which  the  members  call 
upon  the  sick  fund  of  the  society. 

The  following  are  rules  of  individual  hygiene  as  summarized 
from  the  Yale  Lectures  on  Hygiene  by  Professor  L^ing  Fisher, 
190(>-1907:  — 

Air 

Keep  outdoors  as  much  as  possible. 

Breathe  through  the  nose,  not  through  the  mouth. 

When  indoors,  have  the  air  as  fresh  as  possible  — 

(a)  By  having  aired  the  room  before  occupancy. 

(6)  By  having  it  continuously  ventilated  while  occupied. 

Not  only  purity,  but  coolness,  dryness,  and  motion  of  the  air,  if  not  very 
extreme,  are  advantageous.  Air  in  heated  houses  in  winter  is  usually 
too  dry,  and  may  be  humidified  with  advantage. 

Clothing  should  be  sufficient  to  keep  one  warm.  The  minimum  that 
will  secure  this  result  is  the  best.  The  more  porous  your  clothes,  the  more 
the  skin  is  educated  to  perform  its  functions  with  increasingly  less  need 
for  protection.     Take  an  air  bath  as  often  and  as  long  as  possible. 

Water 

Take  a  daily  water  bath,  not  only  for  cleanhness,  but  for  skin  gym- 
nastics. A  cold  bath  is  better  for  this  purpose  than  a  hot  bath.  A  short 
hot  followed  by  a  short  cold  bath  is  still  better.  In  fatigue,  a  very  hot 
bath  lasting  only  half  a  minute  is  good. 

A  neutral  bath,  beginning  at  97"*  or  98",  dropping  not  more  than  5**, 
and  continued  15  minutes  or  more  is  an  excellent  means  of  resting  the  nerves. 

Be  sure  that  the  water  you  drink  is  free  from  dangerous  germs  and 
impurities.  "  Soft  "  water  is  better  than  "  hard  "  water.  Ice  water 
should  be  avoided  unless  sipped  and  warmed  in  the  mouth.  Ice  may 
contain  spores  of  germs  even  when  germs  themselves  are  killed  by  cold. 

Cool  water  drinking,  including  especially  a  glass  half  an  hour  before 
breakfast  and  on  retiring,  is  a  remedy  for  constipation. 

Food 

Teeth  should  be  brushed  thoroughly  several  times  a  day,  and  floss  silk 
used  between  the  teeth.  Persistence  in  keeping  the  mouth  clean  is  not 
only  good  for  the  teeth,  but  for  the  stomach. 

Masticate  all  food  up  to  the  point  of  involuntary  swallowing,  with  the 
attention  on  the  taste,  not  on  the  mastication.     Food  should  simply  be 


426  HEALTH  AND  DISEASE 

chewed  and  relished,  with  no  thought  of  swallowing.  There  should  be 
no  more  effort  to  prevent  than  to  force  swallowing.  It  will  be  found  that 
if  you  attend  only  to  the  agreeable  task  of  extracting  the  flavors  of  your 
food,  Nature  will  take  care  of  the  swallowing,  and  this  will  become,  like 
breathing,  involuntary.  The  more  you  rely  on  instinct,  the  more  normal, 
stronger,  and  surer  the  instinct  becomes.  The  instinct  by  which  most 
people  eat  is  perverted  through  the  "  hurry  habit  "  and  the  use  of  abnor- 
mal foods.  Thorough  mastication  takes  time,  and  therefore  one  must 
not  feel  hurried  at  meals  if  the  best  results  are  to  be  secured. 

Sip  liquids,  except  water,  and  mix  with  saliva  as  though  they  were 
solids. 

The  stopping  point  for  eating  should  be  at  the  earliest  moment  when 
one  is  really  satisfied. 

The  frequency  of  meals  and  time  to  take  them  should  be  so  adjusted 
that  no  meal  is  taken  before  a  previous  meal  is  well  out  of  the  way,  in  order 
that  the  stomach  may  have  had  time  to  rest  and  prepare  new  juices.  Nor- 
mal appetite  is  a  good  guide  in  this  respect.  One's  best  sleep  is  on  an 
empty  stomach.  Food  puts  one  to  sleep  by  diverting  blood  from  the  head, 
but  disturbs  sleep  later.  Water,  however,  or  even  fruit  may  be  taken 
before  retiring  without  injury. 

An  exclusive  diet  is  usually  unsafe.  Even  foods  which  are  not  ideally 
the  best  are  probably  needed  when  no  better  are  available,  or  when  the 
appetite  especially  calls  for  them. 

The  following  is  a  very  tentative  list  of  foods  in  the  order  of  excellence 
for  general  purposes,  subject,  of  course,  to  their  palatability  at  the  time 
eaten:  fruits,  nuts,  grains  (including  bread),  butter,  buttermilk,  salt  in 
small  quantities,  cream,  milk,  potatoes,  and  other  vegetables  (if  fiber  is 
rejected),  eggs,  custards,  digested  cheeses  (such  as  cottage  cheese,  cream 
cheeses  pineapple  cheese,  Swiss  cheese,  Cheddar  cheese,  etc.),  curds,  whey, 
vegetables,  if  fiber  is  swallowed,  sugar,  chocolate,  and  cocoa,  putrefactive 
cheeses  (such  as  Limburger,  Rochefort,  etc.),  fish,  shellfish,  game,  poultry, 
meats,  liver,  sweetbreads,  meat  soups,  beef  tea,  bouillon,  meat  extracts, 
tea  and  coffee,  condiments  (other  than  salt),  and  alcohol.  None  of  these 
should  be  absolutely  excluded,  unless  it  be  the  last  half  dozen,  which,  with 
tobacco,  are  best  dispensed  with  for  reasons  of  health.  Instead  of  exclud- 
ing specific  food,  it  is  safer  to  follow  appetite,  merely  giving  the  benefit  of 
the  doubt  between  two  foods,  equally  palatable,  to  the  one  higher  in  the 
list.  In  general,  hard  and  dry  foods  are  preferable  to  soft  and  wet  foods. 
Use  some  raw  foods  —  nuts,  fruits,  salads,  milk,  or  other  —  daily. 

The  amount  of  proteid  required  is  much  less  than  ordinarily  consumed. 
Through  thorough  mastication  the  amount  of  proteid  is  automatically 
reduced  to  its  proper  level. 

The  sudden  or  artificial  reduction  in  proteid  to  the  ideal  standard  is 
apt  to  produce  temporarily  a  **  sour  stomach,"  unless  fats  be  used  abun- 
dantly. 


HEALTH  AND  DISEASE  427 

To  balance  each  meal  is  of  the  utmost  importance.  When  one  can  trust 
the  appetite,  it  is  an  almost  infallible  method  of  balancing,  but  some 
knowledge  of  foods  will  help.  The  aim,  however,  should  always  be  — 
and  this  cannot  be  too  often  repeated  —  to  educate  the  appetite  to 
the  point  of  deciding  all  these  questions  automatically. 

Exercise  and  Rest 

The  hygienic  life  should  have  a  proper  balance  between  rest  and  exer- 
cise of  various  kinds,  physical  and  mental.  Generally  every  muscle  in  the 
body  should  be  exercised  daily. 

Muscular  exercise  should  hold  the  attention,  and  call  into  play  will 
power.     Exercise  should  be  enjoyed  as  play,  not  endured  as  work. 

The  most  beneficial  exercises  are  those  which  stimulate  the  action  of 
the  heart  and  lungs,  such  as  rapid  walking,  running,  hill  climbing,  and 
swimming. 

The  exercise  of  the  abdominal  muscles  is  the  most  important  in  order  to 
give  tone  to  those  muscles  and  thus  aid  the  portal  circulation.  For  the 
same  reason  erect  posture,  not  only  in  standing,  but  in  sitting,  is  important. 
Support  the  hollow  of  the  back  by  a  cushion  or  otherwise. 

Exercise  should  always  be  limited  by  fatigue,  which  brings  with  it 
fatigue  poisons.  This  is  nature's  signal  when  to  rest.  If  one's  use  of  diet 
and  air  is  proper,  the  fatigue  point  will  be  much  further  off  than  other- 
wise. 

One  should  learn  to  relax  when  not  in  activity.  The  habit  produces 
rest,  even  between  exertions  very  close  together,  and  enables  one  to  con- 
tinue to  repeat  those  exertions  for  a  much  longer  time  than  otherwise. 
The  habit  of  lying  down  when  tired  is  a  good  one. 

The  same  principles  apply  to  mental  rest.  Avoid  worry,  anger,  fear, 
excitement,  hate,  jealousy,  grief,  and  all  depressing  or  abnormal  mental 
states.  This  is  to  be  done  not  so  much  by  repressing  these  feelings  as  by 
dropping  or  ignoring  them  —  that  is,  by  diverting  and  controlling  the  atten- 
tion. The  secret  of  mental  hygiene  lies  in  the  direction  of  attention. 
One's  mental  attitude,  from  a  hygienic  standpoint,  ought  to  be  optimistic 
and  serene,  and  this  attitude  should  be  striven  for  not  only  in  order  to  pro- 
duce health,  but  as  an  end  in  itself,  for  which,  in  fact,  even  health  is  properly 
sought.  In  addition,  the  individual  should,  of  course,  avoid  infection, 
poisons,  and  other  dangers. 

Occasional  physical  examination  by  a  competent  medical  examiner  is  ad- 
visable.    In  case  of  illness,  competent  medical  treatment  should  be  sought. 

Finally,  the  duty  of  the  individual  does  not  end  with  personal  hygiene. 
He  should  take  part  in  the  movements  to  secm-e  better  public  hygiene 
in  city,  state,  and  nation.  He  has  a  selfish  as  well  as  an  altruistic  motive 
to  do  this.  His  air,  water,  and  food  depend  on  health  legislation  and  ad- 
ministration. 


428 


HEALTH  AND  DISEASE 


All  the  foregoing  rules  are  important.  The  results  which  may- 
be obtained  by  following  them  depend  largely  on  the  thorough- 
ness with  which  they  are  followed.  This  is  true  especially  of 
fresh  air  and  mastication.  If  all  the  rules  are  followed  and 
followed  thoroughly,  including  the  one  most  commonly  neglected, 
—  namely,  keeping  within  the  fatigue  limit,  —  the  average  man 
may  reasonably  expect  to  double  his  length  of  life,  his  activity 
per  day,  his  satisfactions  and  his  usefulness.  The  laws  of 
"  humaniculture  "  can  be  depended  upon  as  much  as  those  of 
agriculture,  horticulture,  or  §tock  raising. 

Public  Hygiene.  —  Although  it  is  absolutely  necessary  for  each 
individual  to  obey  the  laws  of  health  if  he  or  she  wishes  to  keep 

from  disease,  it  has  also 
become  necessary,  es- 
pecially in  large  cities, 
to  have  general  super- 
vision over  the  health 
of  people  living  in  a 
community.  This  is 
done  by  means  of  a 
department  or  board 
of  health.  It  is  the 
function  of  this  de- 
partment to  care  for 
public  health.  A  list 
of  regulations  and  laws 
known  as  the  Sanitary 
Code  is  given  out  to 
the  citizens.  These 
regulations  concern  the 
care  of  buildings  and 
plumbing,  of  the  clean- 
liness of  street  cars 
and  other  public  vehi- 
cles, the  protection  and 
supervision  of  foods  sold,  the  inspection  of  our  supplies  of  milk 
and  water,  and  particularly,  the  control  of  disease. 

Examples  of  what  public  control  of  disease  will  do  is  seen  when 


-400 
-300 
-400 

\ 

■^ 

\ 

s 

\ 

^ 

.100 

18 

50     ISfeO,    18T0      1880     la'go     190019061 

The  curve  showing  a  decreasing  death  rate  from  tu- 
berculosis. Why  do  fewer  people  die  from  the 
disease  than  formerly  ? 


HEALTH  AND   DISEASE 


429 


we  consider  the  specific  case  of  the  disease  known  as  smallpox.  In 
the  eighteenth  century  5,000,000  people  are  said  to  have  died  from 
it;  one  hundred  years  ago  it  was  exceedingly  common  in  all  large 
cities  in  this  country.  To-day  an  epidemic  of  smallpox  is  impos- 
sible, thanks  to  the  discovery  of  vaccination  and  prompt  action  by 
the  health  department.  Tuberculosis  at  the  present  time  kills  more 
people  annually  than  any  other  disease,  and  yet  it  is  believed  by 
sanitary  living  we  will  stamp  out  the  disease  within  fifty  years  if 


Deaths  from  tuberculosis  contrasted  with  the  other  contagious  diseases  in 
the  center  of  New  York  in  1908. 

we  go  on  at  the  present  rate.  Public  hygiene  is  largely  responsible 
for  the  lessening  of  deaths  from  typhoid  fever  and  other  diseases 
which  are  transmitted  through  the  milk  or  water  supply.  It  is 
estimated  that  pure  milk,  pure  water,  and  pure  air  supplied  to  all 
would  lengthen  the  average  human  life  in  the  United  States  eight 
years.  At  the  present  rate  human  life  is  being  lengthened  about 
14  years  every  century  in  Massachusetts,  17  in  Europe,  and  27 
per  century  in  Prussia.^  In  India,  on  the  other  hand,  where  little 
hygiene  is  known  or  practiced  among  the  masses  of  people,  the 
length  of  life  is  stationary. 

1  This  result  is  obtained  by  the  saving  of  the  lives  of  thousands  of  young  children, 
who  now  grow  to  become  adults. 


430  HEALTH  AND  DISEASE 

Ex-President  Roosevelt  said  in  one  of  his  latest  messages  to 
Congress :  — 

'*  There  are  about  3,000,000  people  seriously  ill  in  the  United  States,  of 
whom  500,000  are  consumptives.  More  than  half  of  this  illness  is  prevent- 
able. If  we  count  the  value  of  each  life  lost  at  only  $1700  and  reckon  the 
average  earning  lost  by  illness  at  $700  a  year  for  grown  men,  we  find  that 
the  economic  gain  from  mitigation  of  preventable  disease  in  the  United 
States  would  exceed  $1,500,000,000  a  year.  This  gain  can  be  had  through 
medical  investigation  and  practice,  school  and  factory  hygiene,  restriction 
of  labor  by  women  and  children,  the  education  of  the  people  in  both  pub- 
lic and  private  hygiene,  and  through  improving  the  efficiency  of  our  health 
service,  municipal,  state,  and  national." 

Infectious  Diseases  and  Quarantine.  —  One  of  the  important 
means  for  prevention  of  the  spread  of  diseases  caused  by  bacteria 
or  Protozoa  is  by  quarantine.  The  board  of  health  at  once  isolates 
any  case  of  disease  which  may  be  communicated  from  one  person  to 
another.  This  is  called  quarantine.  No  one  save  the  doctor  or 
nurse  should  enter  the  room  of  the  person  quarantined.  After  the 
disease  has  run  its  course,  the  clothing,  bedding,  etc.,  in  the  sick 
room  is  fumigated.  This  is  usually  done  by  the  board  of  health. 
Formaldehyde  in  the  form  of  candles  for  burning  or  in  a  liquid 
form  is  a  good  disinfectant.  The  room  should  be  tightly  closed 
to  prevent  the  escape  of  the  gas  used,  as  the  object  of  the  disin- 
fection is  to  kill  all  the  disease  germs  left  in  the  room. 

Immunity.  —  In  the  prevention  of  germ  diseases  we  must  fight  the 
germ  by  attacking  the  parasites  directly  with  poisons  that  will  kill 
them  (such  poisons  are  called  germicides  or  disinfectants),  and 
we  must  strive  to  make  the  persons  coming  in  contact  with  the 
disease  unlikely  to  take  it.  This  insusceptibility  or  immunity 
may  be  either  natural  or  acquired.  Natural  immunity  seems  to  be 
in  the  constitution  of  a  person,  and  may  be  inherited.  Immunity 
may  be  acquired  by  means  of  such  treatment  as  the  antitoxin 
treatment  for  diphtheria.  This  treatment,  as  the  name  denotes, 
is  a  method  of  neutralizing  the  poison  (toxin)  caused  by  the  bacteria 
in  the  system.  It  was  discovered  a  few  years  ago  by  a  German, 
Von  Behring,  that  the  serum  of  the  blood  of  an  animal  immune 
to  diphtheria  is  capable  of  neutralizing  the  poison  produced  by 
the  diphtheria-causing  bacteria.      Horses  are  rendered  immune 


HEALTH  AND  DISEASE 


431 


by  giving  them  gradually  larger  doses  of  the  diphtheria  toxin  or 
poison.  The  serum  (or  liquid  part)  of  the  blood  of  these  horses  is 
then  used  to  inoculate  the  patient  suffering  from  or  exposed  to 
diphtheria,  and  thus  the  disease  is  checked  or  prevented  altogether 
by  the  antitoxin  injected  into  the  blood. 

Vaccination.  —  Smallpox  was  once  the  most  feared  disease  in 
this  country;  95  per  cent  of  all  people  suffered  from  it.  As  late 
as  1898,  over  50,000  persons  lost  their  lives  annually  in  Russia  from 

this  disease.  It  is  probably  not  caused 
by  bacteria,  but  by  a  tiny  animal  para- 
site. Smallpox  has  been  brought  under 
absolute  control  by  vaccina- 
tion, —  the  inoculation  of  man 
with  the  substance  (called 
virus)  which  causes  cowpox  in 
a  cow.  Cowpox  is  like  a 
mild  form  of  smallpox, 
and  the  introduction  of 
this  virus  gives  complete 
immunity  to  smallpox  for  several  years 
after  vaccination.  This  immunity  is 
caused  by  the  formation  of  a  germicidal 
substance  in  the  blood,  due  to  the  in- 
troduction of  the  virus. 
The  Work  of  the  Department  of  Street  Cleaning.  —  In  any 
city  one  menace  to  the  health  of  its  citizens  exists  in  the  refuse  and 
garbage.  The  city  streets,  when  dirty,  contain  countless  millions 
of  germs  which  have  come  from  decaying  material,  or  from  people 
ill  with  disease.  In  most  large  cities  a  department  of  street 
cleaning  not  only  cares  for  the  removal  of  dust  from  the  streets, 
but  also  has  the  removal  of  garbage,  ashes,  and  other  waste  as  a 
part  of  its  work.  The  practice  of  putting  open  cans  contain- 
ing ashes  and  garbage  into  the  street  for  disposal  is  an  indirect 
means  of  spreading  disease,  for  flies  breed  and  germs  may  thrive 
there.  The  street-cleaning  department  should  be  aided  by  every 
citizen;  rules  for  the  separation  of  garbage,  papers,  and  ashes  should 
be  kept.  Garbage  and  ash  cans  should  be  covered.  The  practice 
of  upsetting  ash  or  garbage  cans  is  one  which  no  young  citizen  should 


A  bad  condition  of  the  streets, 
lower  East  Side,  New  York. 


432  HEALTH  AND  DISEASE 

allow  in  his  neighborhood,  for  sanitary  reasons.  The  best  results 
in  summer  street-cleaning  are  obtained  by  washing  or  flushing  the 

Removal  of    ashes   by    department   of    street     great     tanks  ;      from     this 

cleaning.  New  York.  material  the   fats  are  ex- 

tracted, and  the  soHd  matter  is  sold  for  fertilizer.  Ashes  are  used 
for  filling  marsh  land.  Thus  the  removal  of  waste  matter  may 
p&y  for  itself  in  a  large  city. 

The  Necessity  of  a  Pure  Milk  and  Water  Supply.  —  The  city  of 
New  York  is  spending  hundreds  of  millions  of  dollars  to  bring  a 
supply  of  pure  water  to  her  citizens.  Other  cities  are  doing  the 
same.  The  world  has  awakened  to  the  necessity  of  a  pure  water 
supply,  largely  because  of  the  number  of  epidemics  of  typhoid 
which  have  been  caused  by  contaminated  water.  Typhoid  fever 
germs  live  in  the  food  tube,  hence  the  excreta  of  a  typhoid  patient 
will  contain  large  numbers  of  germs.  In  a  city  with  a  system  of 
sewage  such  germs  might  eventually  pass  from  the  sewers  into  a 
river.  Many  cities  take  their  water  supply  directly  from  rivers, 
sometimes  not  far  below  another  large  town.  Such  cities  must 
take  many  germs  into  their  water  supply.  Many  cities,  as  Cleve- 
land and  Buffalo,  take  their  water  from  lakes  into  which  their 
sewage  flows.  In  cities  which  drain  their  sewage  into  rivers  and 
lakes,  the  question  of  sewage  disposal  is  a  large  one,  and  many 
cities  now  have  means  of  disposing  of  their  sewage  in  some  manner 
as  to  render  it  harmless  to  their  neighbors.  Filtering  such  water  by 
means  of  passing  the  water  through  settling  basins  and  sand  filters 
removes  about  98  per  cent  of  the  germs.  The  result  of  drinking 
unfiltered  and  filtered  water  in  certain  large  cities  is  shown  graphi- 
cally on  the  following  page. 

In  the  country  typhoid  may  be  spread  by  the  germs  getting  into 
a  well  or  spring  from  whence  the  supply  of  water  comes.    This 


HEALTH  AND  DISEASE 


433 


may  be  avoided  by  having  priv- 
ies and  cesspools  some  distance 
from  the  well  and  so  placed 
that  they  will  drain  away  from 
it.  Wells  should  have  a  ce- 
mented cap  around  the  top  so  as 
to  keep  out  surface  water,  as 
germs  rarely  live  long  more 
than  five  feet  below  ground. 

Serious  outbreaks  of  typhoid 
have  been  traced  to  contami- 
nated milk  supplies.  A  case  of 
typhoid  exists  on  a  farm;  the 
sewage  gets  into  the  well  from 
which  water  is  used  for  the 
washing  of  milk  cans.  Typhoid 

germs  thrive  in  milk.  Thus  the  milkman  spreads  disease.  The 
diagram  following  illustrates  a  recent  epidemic  in  Stamford,  Conn., 
which  was  traced  to  a  farm  on  which  was  a  person  having  typhoid. 


Growth  of  bacteria  in  a  drop  of  impure 
water  allowed  to  run  down  a  sterilized 
culture  in  a  dish. 


20       40        (BO        ao       100     120      140      160      laO     200   220 

A 

1906 

1 

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Cases  of  typhoid  per  100,000  inhabitants  before  filtering  water  supply  (solid)  and 
after  (shaded)  in  A,  Watertown,  N.Y.;  B,  Albany,  N.Y.;  C,  Lawrence,  Mass.; 
D,  Cincinnati,  Ohio.    What  is  the  effect  of  filtering  the  water  supply  ? 

HUNT.  ES.  BIO.  —  28 


434 


HEALTH  AND  DISEASE 


Railroads  are  often  responsible  for  carrying  typhoid  and  spread- 
ing it.  It  is  said  that  a  recent  outbreak  of  typhoid  in  Scranton, 
Pa.,  was  due  to  the  fact  that  the  excreta  from  a  typhoid  patient 
traveling  in  a  sleeping  car  was  washed  by  rain  into  a  reservoir  near 
which  the  train  was  passing.  Railroads  are  thus  seen  to  be  great 
open  sewers.  Some  more  sanitary  kind  of  toilet  should  be  used 
so  that  filth  and  disease  will  not  be  scattered  over  the  country. 


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A  diagram  to  show  how  typhoid  may  be  spread  in  a  city  through  an  infected  milk 
supply.  The  black  spots  in  the  blocks  mean  cases  of  typhoid.  A,  a  farm  where 
typhoid  exists  ;  the  dashes  in  the  streets  represent  the  milk  route.  B  is  a,  second 
farm  which  sends  part  of  its  milk  to  A  ;  the  milk  cans  from  B  are  washed  at 
farm  A  and  sent  back  to  B.  A  few  cases  of  typhoid  appear  along  B's  milk 
route.    How  do  you  account  for  that  ? 

How  the  Board  of  Health  fights  Typhoid.  —  Pure  water  is  the 
first  essential  in  preventing  epidemics  of  typhoid.  Health  board 
officials  are  constantly  testing  the  supply,  and,  if  any  harmful 
bacteria  are  found,  a  warning  is  sent  out  to  boil  the  water.  Boil- 
ing water  at  least  10  minutes  kills  most  harmful  germs. 


HEALTH   AND  DISEASE 


435 


The  milk  supply  is  also  subject  to  rigid  inspection.  Milk  brought 
into  a  city  is  tested,  not  only  for  the  amount  of  cream  present  to 
prevent  dilution  with  water,  but  also  for  the  presence  of  germs. 
Thecleanliuess  of  the  cans,  wapjons,  etc.,  is  also  subject  to  inspection. 


*'  The  patients  live  out  of  doors." 

The  cows  are  also  inspected  to 
see  if  they  have  tuberculosis,  for 
such  cows  might  spread  the  dis- 
ease to  human  beings. 

During  the  summer  months 
many  babies  die  from  cholera 
infantum.  This  disease  is  al- 
most entirely  spread  through 
impure  milk.  Flies  are  largely 
responsible  for  the  spread  of 
the  disease  by  carrying  the 
germs  to  milk.  Spread  of  such  diseases  through  milk  can  only  be 
prevented  by  careful  pasteurization  (heating  to  170  for  a  few 
minutes).  In  many  large  cities  pasteurized  milk  is  sold  at  a 
reasonable  price  to  poor  people,  and  thus  much  disease  is  pre- 
vented. 
Disease  germs  of  various  sorts,  typhoid,  tuberculosis,  pneumonia, 


436  HEALTH  AND  DISEASE 

diphtheria,  and  many  others  may  be  transferred  through  the 
agency  of  food.  Fruits  and  vegetables  may  be  carriers  of  disease, 
especially  if  they  are  sold  from  exposed  stalls  or  cars  and  handled  by 
the  passers-by.  All  vegetables,  fruits,  or  raw  foods  should  be  care- 
fully washed  before  using.  Spoiled  or  overripe  fruit,  as  well  as 
meat  which  is  decayed,  is  swarming  with  bacteria  and  should  not  be 
used.  The  board  of  health  has  supervision  over  the  sale  of  fruit, 
meats,  fish,  etc.,  and  frequently  in  large  cities  food  unfit  for  sale 
is  condemned  and  destroyed. 

How  the  Board  of  Health  fights  Tuberculosis.  —  Tuberculosis, 
which  a  few  years  ago  killed  fully  one  seventh  of  the  people  who 
died  from  disease  in  this  country,  now  kills  less  than  one  tenth.  This 
decrease  has  been  largely  brought  about  because  of  the  treatment 
of  the  disease.  Since  it  has  been  proved  that  tuberculosis  if  taken 
early  enough  is  curable,  by  quiet  living,  good  food,  and  'plenty  of 
fresh  air  and  light,  we  find  that  numerous  sanatoria  have  come  into 
existence  which  are  supported  by  private  or  public  means.  At 
these  sanatoria  the  patients  live  out  of  doors,  especially  sleep 
in  the  air,  while  they  have  plenty  of  nourishing  food  and  little 
exercise.  In  this  way  and  by  tenement-house  laws  which  require 
proper  air  shafts  and  window  ventilation  in  dwellings,  by  laws 
against  spitting  in  public  places,  and  in  other  ways  the  boards  of 
health  in  our  towns  and  cities  are  waging  war  on  tuberculosis. 

Reference  Books 

Sharpe,  A  Laboratory  Manual  for  the  Solution  of  Problems  in  Biology.    American 

Book  Company. 
Allen,  Civics  and  Health.     Ginn  and  Company. 

Davison,  The  Human  Body  and  Health.     American  Book  Company. 
Gulick  Hygiene  Series,  Town  and  City.     Ginn  and  Company. 
Hough  and  Sedgwick,  The  Human  Mechanism.     Ginn  and  Company. 
Richman  and  Wallach,  Good  Citizenship.     American  Book  Company. 
Ritchie,  Primer  of  Sanitation.     World  Book  Company, 

Reports,  etc. 

American  Health  Magazine. 

Annual  Report  of  Department  of  Health,  City  of  New  York  (and  other  cities). 
Bulletins  and  Publications  of  Committee  of  One  Hundred  on  National  Health. 
School  Hygiene,  American  School  Hygiene  Association. 


INDEX 


(Illustrations  are  indicated  by  page  numerals  in  bold-faced  type.) 


Accommodation  of  eye,  410. 
Acts,  automatic,  404. 
Adaptation,  28,  41,  221. 
Adaptations,  for  pollination,  44,  46 ; 

for  seed  dispersal,  53,  54,  56,  66, 
80; 

in  birds,  297,  299,  301 ; 

in  frogs,  285 ; 

in  mammalia,  312 ; 

in  snakes,  295 ; 

in  turtles,  293 ; 

in  vertebral  column,  326 ; 

to  environment,  144,  249. 
Adenoids,  eflfects  of,  389. 
Aggressive  resemblance,  250,  261. 
Air,  amount  of,  in  breathing,  384, 
386; 

changed  in  lungs,  385 ; 

composition  of,  17 ; 

factor  in  germination,  76  ; 

fresh,  how  to  get,  419 ; 

necessity  of,  405. 
Alcohol,  and  abihty  to  do  work,  413 ; 

and  disease,  412,  422 ; 

and  longevity,  424 ; 

a  poison,  345 ; 

as  a  food,  344,  346  ; 

effect  on  blood,  379 ; 

effect  on  bodily  heat,  395 ; 

effect  on  circulation,  379 ; 

effect  on  digestion,  364  ; 

effect  on  excretion,  397 ; 

effect  on  intellectual  ability,  413 ; 

effect  on  leucocytes,  423  ; 

effect  on  respiration,  395 ; 

in  patent  medicines,  350 ; 

in  treatment  of  disease,  422 ; 

paralyzes  nervous  system,  411. 

Alcoholic  poisoning,  economic,  moral, 

and  social  effects  of,  416 : 


AlgaB,  145. 

Alimentary  canal,  362. 
Alligator,  296. 

Alternation  of  generations,  in  coelen- 
terates,  208 ; 

in  fern,  155 ; 

in  mosses,  153 ; 

in  spermatophytes,  156. 
Alveoli,  383. 
Amoeba,  parts  of,  193 ; 

reproduction  of,  193. 
Amphibia,  285 ; 

characteristics  of,  292 ; 

classification  of,  292. 
Angiosperms,  157. 
Animals,  cold-blooded,  369 ; 

domestication,  316 ; 

relation  of,  to  man,  14. 
Annulata,  classification  of,  220. 
Antennae,  223,  244. 
Antennules,  223. 
Antheridia,  153,  166. 
Antherozoid,  defined,  154,  166. 
Ants,  255 ; 

and  their  "cows,"  266; 

artificial  nest  for,  256. 
Aphids  and  ants,  256. 
Appendages  of  skeleton,  327. 
Arachnida,  245,  247. 
Archegonium,  153,  166. 
Arteries,  structure  of,  374. 
Arthropoda,  classified,  247. 
Asexual  reproduction,  amoeba,  193 

in  coelenterates,  208,  209 ; 

in  fern,  155 ; 

in  hydra,  203 ; 

in  mold,  150 ; 

in  moss,  152 ; 

in  paramoecium,  192 ; 

in  Spirogyra,  148. 


437 


438 


INDEX 


Asymmetry  in  oyster,  268. 
Atwater's  experiments,  332. 
Auricle,  370. 

Bacillus,  175. 

Bacteria,  and  fermentation,  177 ; 

carried  by  fly,  260,  261,  420 ; 

cause  decay,  177 ; 

cause  disease,  178 ; 

from  human  mouth,  179 ; 

in  impure  water,  433 ; 

in  milk,  180 ; 

in  schoolroom,  387 ; 

in  streets,  419 ; 

nitrogen-fixing,  178; 

size  and  form,  175  ; 

their  relation  to  man,  14. 
Bacteriology,  defined,  14. 
Bark,  use  of,  104. 
Balanced  aquarium,  185. 
Balancing  in  birds,  300. 
Bean,  65. 

Bean  seedlings,  78. 
Beans,  as  food,  68. 
Beaver,  314. 
Bees,  40,  43,  253,  254. 
Beer  making,  172. 
Beetle,  characters  of,  242. 
Benedict's  test,  71. 
Berry,  53,  63. 
Bile,  functions  of,  360. 
Biology,  civic,  418 ; 

reasons  for  study  of,  13. 
Bird,  body  of,  297. 
Birds,  care  of  young,  304 ; 

classification  of,  308,  311 ; 

distribution  of,  307 ; 

economic  importance  of,  304  ; 

extermination  of,  306 ; 

feathers  of,  298  ; 

feet  of,  299 ; 

flight  of,  298 ; 

migrations  of,  307 ; 

nesting  habits  of,  303,  304 ; 

perching,  309 ; 

perching  in,  300. 
Bison,  315. 
Bladder,  urinary,  391. 
Bladderwort,  130. 
Blastula,  200. 


Blood,  amount  of,  369 ; 

and  its  circulation,  366 ; 

changes  in,  in  body,  393 ; 

changes  in,  in  lungs,  383,  386 ; 

clotting  of,  367 ; 

course  of,  372 ; 

distribution  of,  369 ; 

exchange  in,  376 ; 

function  of,  366  ; 

temperature  of,  369 ; 

vessels,  congestion  in,  394 ; 

wastes  of,  to  kidney,  391. 
Bodily  heat,  affected  by  alcohol,  395 ; 

in  cold-blooded  animals,  393  ; 

regulation  of,  392. 
Body,  daily  fuel  needs  of,  337 ; 

normal  heat  output  of,  339. 
Box  elder  twigs,  sections  of,  103. 
Brain,  functions  of  parts,  403 ; 

of  man,  401. 
Bread  mold,  149 ; 

growth  of,  150. 
Breathing,  and  lacing,  388 ; 

hygienic  habits  of,  388 ; 

mechanics  of,  384 ; 

movements  in,  383,  384 ; 

rate  of,  384. 
Bronchi,  382. 

Bruises,  treatment  of,  378,  394. 
Bryophytes,  157. 
Bud,  structure  of,  98,  99. 
Budding,  110. 
Buds,  factors  in  opening  of,  99; 

position  of,  100. 
Bugs,  242,  243. 
Bumblebee,  40,  41,  42,  253. 
Burns,  treatment  of,  394. 
Butterfly,  237 ; 

compared  with  moth,  238. 

Calorie,  defined,  333. 

Calorimeter,  respiration,  332. 

Calyx,  34. 

Cambium  layer,  use  of,  104,  111. 

Canal,  semicircular,  408. 

Capillary  circulation  in  frog's  foot, 

373. 
Carapace,  222. 
Carbohydrates,  24,  331. 
Carbon,  properties  of,  21. 


INDEX 


439 


Carbon  dioxide,  test  for,  22. 
Carnivorous,  defined,  312. 
Catarrh,  389. 
Catkin,  47. 
Cell,  29 ; 

as  a  unit,  194. 
Cell  membrane,  8&. 
Cell  sap,  89. 
CeU  tissue,  205. 
Cells,  206 ; 

sizes  and  shapes  of,  30. 
Centipede,  poisonous,  246. 
Centrum,  327. 
Cephalopods,  270,  273. 
Cephalothorax,  222. 
Cerebellum,  401. 
Cerebrum,  401 ; 

functions  of,  403. 
Cestodes,  217. 
Chelipeds,  222. 

Chemical  element  and  compound,  18. 
Chlorophyll  bands,  147. 
Chlorophyll  bodies  in  leaf,  120. 
Chromosomes,  29. 
Chrysalis,  237,  238. 
Cicada,  242,  243. 
Cilia,  191. 
Circulation,  effects  of  alcohol  on,  379 ; 

effect  of  exercise  on,  377 ; 

effect  of  tobacco  on,  381 ; 

in  a  mammal,  372 ; 

in  capillaries,  373,  374  ; 

in  crayfish,  225 ; 

in  fishes,  279 ; 

in  frog,  287,  373 ; 

in  kidney,  391 ; 

in  man,  370 ; 

organs  of,  206 ; 

portal,  362,  372 ; 

pulmonary,  372 ; 

systemic,  372. 
Clam,  fresh-water,  shell  of,  268 ; 

round,  parts  of,  269. 
Class,  defined,  157. 
Club  mosses,  156. 
Coelenterates,  207,  208,  209 ; 

compared  with  worms,  215. 
Colds,  cause  of,  394. 
Coleoptera,  242,  247. 
Colloid,  defined,  358. 


Combustion,  22. 

Composite  head,  parts  of,  44, 

Conjugation,  148,  160; 

in  black  mold,  160 ; 

in  paramcecium,  192. 
Contagious     diseases,     death     rafte 

from,  429. 
Copepod,  231. 
Coral,  madreporic,  209. 
Coral  reefs,  210. 
Corn,  grain  of,  69 ; 

production  of,  68. 
Corn  grain,  foods  in,  70,  73. 
Corn  smut,  174. 
Corolla,  34. 
Corpuscle,  red,  function  of,  367; 

structure  of,  367. 
Corpuscle, colorless,  functions  of,  388 ; 

structure  of,  367,  368. 
Corpuscles,  tactile,  321,  406. 
Cortex,  87 ; 

in  stem,  103. 
Cotton,  61. 

Cotton  boll  weevil,  62,  262. 
Cotyledons,  as  foliage  leaves,  79 ; 

food  in,  66 ; 

functions  of,  79 ; 

in  bean,  66 ; 

of  corn,  69. 
Crab,  blue,  229 ; 

fiddler,  229 ; 

giant  spider,  230 ; 

hermit,  229. 
Crayfish,  adaptation  for  protection, 
222; 

and  allies,  characters  of,  231 ; 

appendages,  224; 

external  structure,  222 ; 

internal  structure,  226 ; 

senses  of,  223. 
Crops,  rotation  of,  95. 
Cross-pollination,  defined,  38. 
Crustacea,  degenerate,  232. 
Crustaceans,  222 ; 

habitat  of,  231 ; 

parasitic,  232. 
Crystalloid,  defined,  358. 
Culture,  pure,  176. 
Cuts,  treatment  of,  378,  394. 
Cytoplasm,  30, 


440 


INDEX 


Dandelion,  86; 

leaves  of,  118. 
Decay  by  bacteria,  177. 
Deliquescent  tree,  100. 
Dermis,  321. 
Development,  of  bee,  254 ; 

of  crayfish,  226 ; 

of  fly,  241 ; 

of  frog,  288,  289,  290; 

of  lobster,  227 ; 

of  moth,  239. 
Diaphragm,  357 ; 

in  respiration,  384. 
Diastase,  action  of,  72. 
Diatoms,  149. 
Dichogamy,  48. 
Dicotyledons,  73. 
Dietary,  best,  333. 
Digestion,  352 ; 

and  absorption,  352 ; 

effect  of  alcohol  on,  364 ; 

in  corn  grain,  71 ; 

in  crayfish,  225 ; 

in  fishes,  278 ; 

in  plants,  106 ; 

of  starch,  356 ; 

organs  of,  206,  352 ; 

purpose  of,  352. 
Digestive  tract  in  frog,  287. 
Dipnoi,  284. 
Diptera,  240,  241,  242,  247 ; 

prevention  of,  418. 
Disease  of  nose  and  throat,  389. 
Diseases,  due  to  insects,  258,  259, 
260; 

infectious,  430. 
Division  of  labor,  199 ; 

in  hydra,  203 ; 

in  vorticella,  195. 
Dragon  fly,  244. 
Drone,  254. 

Drugs,  use  and  abuse  of,  349. 
Dusting,  387. 

Dyspepsia,    causes   and   prevention 
of,  363. 

Ear,  human,  408. 

Earthworm,  development  of,  215  ; 

locomotion  in,  214 ; 

relation  to  surroundings,  212. 


Eating,  hygienic  habits  of,  363. 
Economic   importance,  of   alcoholic 
poisoning,  416 ; 

of  birds,  304 ; 

of  carnivora,  313 ; 

of  corals,  210 ; 

of  earthworms,  215 ; 

of  ferns,  156 ; 

of  food  in  roots,  95 ; 

of  insects,  261,  262,  263,  264,  265; 

of  leaves,  128 ; 

of  lobster,  228 ; 

of  moUusks,  269,  271 ; 

of  parasitic  worms,  219 ; 

of  plants,  170 ; 

of  roots  and  stems,  109 ; 

of  snakes,  295 ; 

of  starfish,  272 ; 

of  trees,  133,  135. 
Ectoderm,  defined,  200. 
Egg,  development  of,  200. 
Egg  cell,  37,  153,  155,  227,  280,  288. 
Egg-laying  habits  of  fishes,  280. 
Elasmobranch,  283,  284. 
Embryo  sac,  36,  156. 
Endoderm,  defined,  200. 
Endoskeleton,  275,  279. 
Endosperm,  use  of,  69,  72. 
Energy,  defined,  20. 
Entomostraea,  231. 
Environment,  17. 

Enzyme,    action    upon    fibrinogen, 
367; 

in  saliva,  357. 
Enzymes,  72,  353 ; 

in  blood,  366,  367 ; 

in  gastric  juice,  358 ; 

reversible  action  of,  366. 
Epicotyl,  65. 
Epidermis,  321. 
Epiglottis,  354. 
Erosion,  by  streams,  133,   134 ; 

prevented    by    organic    covering, 
135. 
Esophagus,  352,  354,  357. 
Eustachian  tube,  354,  408. 
Excretion,    effect   of   alcohol   upon, 
397; 

in  crayfish,  226 ; 

organs  of,  in  man,  390. 


INDEX 


441 


Excurrent  tree,  100. 
Exercise,  and  health,  421 ; 

in  hygiene,  427. 
Exoskeleton,  222. 
Expiration,  384. 
Eye,  coats  of,  409  ; 

defects  in,  410; 

human,  409 ; 

image  formed  in,  410  ; 

of  crayfish,  223 ; 

of  insect,  236. 

Facets,  236. 

Family,  defined,  157. 

Fatigue,  defined,  378. 

Fats,  24,  331. 

Fermentation,  chemistry  of,  172. 

Ferns,  characteristics  of,  155. 

Fertilization,  37,  155,  153. 

Fevers,  394. 

Fibrin,  367. 

Fibrinogen,  367. 

Fibrovascular  bundles,  88 ; 

of  a  monocotyledon,   108; 

use  of,  101. 
Filament,  34. 
Fisheries  of  world,  282. 
Fishes,  appendages  of,  276 ; 

body  of,  275 ; 

classification  of,  283 ; 

migration  of,  282 ; 

protection  of,  283. 
Fission,  30,  192. 
Flatworms,  216. 
Flower,  color  and  odor  of,  41 ; 

dimorphic,  49 ; 

fertilization  of,  36 ; 

pistillate,  47,  68 ; 

relation  to  fruit,  65 ; 

staminate,  46,  47,  68 ; 

structure  of,  34 ; 

trimorphic,  49. 
Prowers,  work  of,  34. 
Fly,  foot  of,  241 ; 

typhoid,  240,  260. 
Food,  24 ; 

and  dietaries,  330 ; 

and  health,  420 ; 

discovery  of  value  of,  332 ; 

economy,  337 ; 


Food,  in  hygiene,  425 ; 

laws,  343 ; 

necessity  of,  405 ; 

storage  in  stem,  109 ; 

swallowing  of,  357 ; 

vacuoles,  191,  193 ; 

values,  340,  341 ; 

waste  in  kitchen,  342 ; 

why  we  need,  330. 
Food  taking,  in  clams,  267 ; 

in  crajiish,  223 ; 

in  earthworm,  214 ; 

in  fishes,  279 ; 

in  hydra,  202 ; 

in  insects,  235 ; 

in  snakes,  295 ; 

in  the  starfish,  272 ; 

in  turtles,  293 ; 

organs  of,  206. 
Foods,    absorbed    into    blood,    361, 
362; 

adulterations  in,  343 ; 

costs  of  various,  338 ; 

inorganic,  24,  331 ; 

in  roots  and  stem,  110 ; 

organic,  23 ; 

values  of,  336. 
Foraminifera,  198. 
Forest  destruction,  139,  140. 
Forest    regions    in    United    States, 

136. 
Forestry,  141. 
Forests,  protection  of,  141 ; 

their  uses  and  protection,  133. 
Fowls,  309. 
Frog,  leopard,  286 ; 

study  of,  285 ; 

tree,  291. 
Frond,  164. 
Fruit,  51. 
Fruits,  and  their  uses,  51 ; 

economic  value  of,  57 ; 

garden,  63 ; 

orchard,  63. 
Function,  defined,  27. 
Functions,  of  an  animal,  27,  206; 

of  parts  of  a  plant,  26. 
Fungi,  149; 

parasitic,  173,  174; 

saprophytic,  171,  172. 


442 


INDEX 


GaU-bladder,  352,  360. 
Gametophyte,  152,  153,  155. 

in  fern,  155 ; 

in  moss,  152. 
Ganglia,  399. 
Ganoid,  283,  284. 
Gastric  juice,  358. 
Gastric  mill,  225. 
Gastropods,  270,  273. 
Gastrula,  200. 
Genus,  defined,  157. 
Geotropism,  85. 
Germination,  defined,  74 ; 

factors  in,  74 ; 

of  bean,  78. 
Gila  monster,  294. 
Gill  rakers,  277. 
Gills,  fish's,  structure  of,  277. 
Girdle,  pectoral,  in  man,  327 ; 

pelvic,  in  man,  327. 
Glands,  gastric,  358; 

intestinal,  360 ; 

lymph,  377  ; 

mesenteric,  363 ; 

salivary,  356 ; 

structure  of,  353 ; 

sweat,  391. 
Glomerulus,  391. 
Glottis  of  man,  354. 
Glycogen,  formation  of,  360. 
Grafting,  111. 
Grain,  56. 

Grape  sugar,  tests  for,  70,  71. 
Guard  cells,  120. 
Gullet,  352,  354. 
Gymnosperms,  157. 

Habits,  formation  of,  404 ; 

importance  of  right,  404. 
Hasmoglobin,  368. 
Hair  protection,  in  leaves,  129. 
Hairs,  development  of,  321. 
Halophytes,  161. 
Hay  infusion,  life  in,  188. 
Health,  and  disease,  418 ; 

department  of,  434,  436. 
Hearing,  organ  of,  407,  408. 
Heart,  a  force  pump,  371. 
Heart,  in  action,  371 ; 

nervous  control  of,  377 ; 


Heart,  position  of,  370 ; 

protection  of,  370 ; 

structure  of,  370 ; 

valves  in,  370,  371. 
Heliotropism,  116,  117. 
Hemiptera,  242,  247. 
Honeybee,  253. 
Hookworm,  217,  218. 
Hornets'  nest,  254. 
Horny  fiber  sponge,  201. 
Horse,  geologic  history,  316. 
Human  blood,  367. 
Human  body  a  machine,  320. 
Humus,  21,  92. 
Hybridizing,  82. 
Hydra,  202. 
Hydrogen,  21. 
Hydroid  colony,  208. 
Hydrophytes,  160. 
Hygiene,  personal,  418; 

public,  428. 
Hymenoptera,  245,  247. 
Hypha,  149. 
Hypocotyl,  65. 

Ichneumon  fly,  257. 

Immunity,  430. 

Inorganic  soil,  relation  to  organic, 

92. 
Insects,  233 ; 

and  crustaceans  compared,  246 ; 

beneficial,  264 ; 

communal  life,  252 ; 

control  of  damage  by,  265 ; 

disease-carrying,    258,    259,    260, 
261; 

divisions  of,  247 ; 

noxious,  262,  263,  264 ; 

relation  to  mankind,  258 ; 

winners  in  life's  race,  233. 
Inspiration,  384. 
Instincts,  312. 
Intestine,  large,  363 ; 

small,  structure  of,  361. 
Irritability,  defined,  32. 
Invertebrate,  cross  section  of,  274. 

Joint,  hinge,  324. 

Key  fruit,  56. 


INDEX 


443 


Kidney,  human,  390. 
Knots,  cause  of,  139. 

Lacteals,  361,  362,  377. 
Larval  stages,  defined,  200, 
Larynx,  364. 

Lateral  line,  function  of,  276. 
Leaf,  cell  structure  of,  120 ; 

functions  of,  128 ; 

respiration  in,  128 ; 

structure  of,  119. 
Leaves,  as  holdfasts,  113; 

arrangement  of,  118 ; 

as  insect  traps,  130,  131  ; 

climbing,  130; 

modified,  129,  130,  131 ; 

reduced,  130. 
Lens  of  eye,  410. 
Lenticels,  use  of,  102. 
Lepidoptera,  247. 
Leucocytes,  alcohol  upon,  423. 
Levers,  classes  of,  326 ; 

in  body,  324. 
Lichens,  187. 
Life  history,  of  beetle,  242 ; 

of  butterfly,  237 ; 

of  Cecropia,  239 ; 

of  cicada,  243 ; 

of  fly,  240,  241 ; 

of  frog,  288,  289.  290 ; 

of  honeybee,  254 ; 

of  locust,  236 ; 

of  shrimp,  227. 
Light,  effect   of,   upon   plants,    116, 

116,  117. 
Lily,  leaves  of,  118. 
Liver,  362,  360. 

Living  matter,  composition  of,  23. 
Living  things,  environment  of,  17 ; 

functions  and  composition  of,  26. 
Lizards,  294. 

Lobster,  North  American,  226. 
Locomotion,  in  crayfish,  222 ; 

in  frogs,  286 ; 

in  snakes,  295 ; 

of  earthworm,  214. 
Locust,  234 ; 

relatives  of,  236. 
Locule,  37. 
Lumber,  transportation  of,  137,  138. 


Lymph,  function  of,  375. 
Lymph  vessels,  376. 

Macronucleus,  192. 
Malacostraca,  247. 
Malaria  and  the  mosquito,  197,  258. 
Mammal,  circulation  in,  372 ; 

man  a,  319. 
Mammals,  311 ; 

classification  of,  317 ; 

hoofed,  316. 
Man,  brain  of,  401 ; 

circulation  in,  370  ; 

evolution  of,  319; 

place  of,  in  nature,  319; 

races  of,  320 ; 

stomach  of,  363,  367. 
Mantis,  261. 
Mantle  cavity,  267. 
Maxillipeds,  224. 
May  flies,  245. 
MeduUa,  401. 
Medusa,  207,  208. 
Membrane,  tympanic,  407. 
Mesoderm,  200. 
Mesophytes,  162. 
Metamorphosis,  defined,  247. 
Metazoa,  199. 
Micronucleus,  192. 
Micropyle,  of  bean,  65 ; 

of  ovule,  36. 
Mildews,  174. 
Milk,  an  emulsion,  369 ; 

and  typhoid,  434 ; 

bacteria  in,  180 ; 

necessity  of  pure,  432,  434. 
Milkweed,  dispersal  in,  80. 
Mimicry  in  insects,  261,  262. 
Mineral  matter,  in  Uving  things,  22. 
Molars,  366. 
MoUusks,  classification  of,  273 ; 

habitat  of,  271 ; 

some  common,  268,  269,  270. 
Molting,  228. 

Monarch  butterfly,  237,  261. 
Monocotyledons  73. 
Mosquito  and  malaria,  196 ; 

and  yellow  fever,  259 ; 

kinds  of,  197,  258; 

malarial,  197,  259,  269. 


AAA 


INDEX 


Mosses,  162. 

Mucus,  353. 

Muscle  tissue,  use  of,  323. 

Muscles,  and  skeleton,  324 ; 

arrangement  of  voluntary,  322 ; 

extensor,  322 ; 

flexor,  322 ; 

nerve  endings  in,  323  ; 

structure  of  voluntary,  323. 
Mushrooms,  151. 
Mycelium,  149,  151. 
Myriapods,  246,  247. 

Nails,  development  of,  321, 
Narcotics,  in  common  use,  417. 
Natural  resources,  conservation  of, 

15. 
Nectar  glands,  38,  42. 
Nectar  guides,  42. 
Nerve,  optic,  409 ; 

parts  of,  401. 
Nerve  fibers,  399. 
Nerves,  motor,  401,  402 ; 

sensory,  401,  402 ; 

vasomotor,  377. 
Nervous  control,  of   blood   vessels, 
377; 

of  heart,  377  ; 

of  respiration,  384 ; 

of  stomach,  358 ; 

of  sweat  glands,  392 ; 

organs  of,  206. 
Nervous  system,  and  sense  organs, 
399; 

cerebro-spinal,  400 ; 

divisions  of,  399 ; 

function  of,  328 ; 

governing  stomach,  358 ; 

in  birds,  302 ; 

in  fishes,  279 ; 

in  man,  328 ; 

of  crayfish,  225 ; 

of  frog,  402 ; 

of  insects,  236 ; 

sympathetic,  402,  403. 
Neuroptera,  244,  247. 
Newt,  292. 
Nicotine,  349,  417. 
Nictitating  membrane,  286. 
Nitrogen,  in  air,  17 ; 


Nitrogen,  in  plant  growth,  94  ; 

properties  of,  18. 
Nitrogen  cycle,  186. 
Nitrogen-fixing  bacteria,  94. 
Nucleolus,  29. 
Nucleus,  29  ; 

in  amoeba,  193 ; 

in  paramcecium,  191. 
Nutrients,  24,  330 ; 

fuel  values  of,  333 ; 

in  beans,  67 ; 

uses  of,  332. 
Nymph,  244. 

Oils,  24,  331. 

Ommatidia,  223. 

One-celled  animals,  195. 

Operculum  in  fishes,  277. 

Opium,  417. 

Orchid,  wild,  38. 

Order,  defined,  157. 

Organ,  defined,  26,  204. 

Organic  and  inorganic  matter,  31. 

Organism,  defined,  26. 

Organs  of  a  plant,  27. 

Orthoptera,  247. 

Osculum,  201. 

Osmometer,  potato,  90. 

Osmosis,  90 ; 

importance  of,  91 ; 

of  sugar,  106. 
Ostrich,  African,  308. 
Ovipositor,  234. 
Ovule,  development  of,  into  seed,  37 ; 

fertilization  of,  37. 
Oxidation,  19; 

heat  the  result  of,  20 ; 

in  germination,  77 ; 

in  human  body,  22 ; 

of  carbon,  21 ; 

rapid,  22 ; 

slow,  20. 
Oxygen,  evolved  in  starch  making, 
126,  147 ; 

preparation  of,  18,  19 ; 

properties  of,  19. 
Oyster,  shell  of,  268 ; 

and  typhoid,  269. 

Palate,  hard,  364. 


INDEX 


445 


Palate,  soft,  364. 

Pancreas,  position  of,  362,  359; 

structure  of,  359. 
Pancreatic  juice,  function  of,  360. 
PapillaB,  355. 
Pappus,  64. 
Paramoecium,  191,  192; 

response  to  stimuli  in,  191. 
Parapodia,  216. 
Parasites,  149. 
Parasitism  in  insects,  267. 
Pasteurizing,  178. 
Patent  medicines,  alcohol  in,  360. 
Pearl  formation,  270. 
''Peepers,"  291. 
Pepo,  63. 
Pepsin,  358. 
Peptone,  358 ; 

changed  to  proteid,  366. 
Pericardium,  370. 
Perspiration,  insensible,  392. 
Petal,  34. 
Phagocytes,  369. 
Pharynx,  364. 

Phosphorus,  in  living  matter,  331. 
Photosynthesis,  124. 
Physiology,  human,  defined,  13. 
Pigeon-wheat  moss,  162. 
Pistil,  34,  36. 
Pitcher  plants,  131. 
Plant,  and  animal  compared,  26. 
Plant  body,  simplest,  144. 
Plant  breeding,  81. 
Plant  invasions,  168. 
Plant  life,  in  temperate  zones,  165; 

forms  of,  144 ; 

in  tropics,  164 ; 

upon  mountains,  164. 
Plant  modification,  cold  a  factor  in, 
164; 

water  a  factor  in,  160,  161,  162 ; 

wind  a  factor  in,  163. 
Plant  outpost,  a,  169. 
Plant  societies,  166,  167. 
Plants,  beneficial  and  harmful,  171 ; 

classification  of,  157 ; 

harm  done  by,  170 ; 

modified  by  surroundings,  159, 160  ; 

relations  to  animals,  13,  15,  184, 
185,  186. 


Plasma  of  blood,  366. 
Plasmodium  malaria;,  196. 
Pleura,  383. 
Pleurococcus,  148. 
Plumule,  66. 
Pocket  garden,  85. 
Pollen,  growth  of,  35,  36. 
Pollen,  protection  of,  49. 
Pollination,  38 ; 

artificial,  50 ; 

by  hunmiing  bird,  43 ; 

by  insects,  40 ; 

by  water,  47 ; 

by  wind,  46 ; 

history  of,  37. 
Polycotyledon,  73. 
Polyphemus  moth,  239. 
Polypody,  164. 
Polyps,  coral,  209 ; 

hydroid,  208. 
Pond  lihes,  169. 
Pond  scum,  147. 
Potato  tuber.  111. 
Premolars,  366. 
Proboscis,  43. 

Proglottids  of  tapeworm,  217. 
Prolegs,  238. 
Pronuba,  46. 
Protective  resemblance,  249,  260 

seasonal,  309. 
Proteid  making  in  plant,  124. 
Proteids,  24,  67,  330 ; 

building  of,  106. 
Prothallus,  154,  166. 
Protonema,  153. 
Protoplasm,  composition  of,  31 ; 

properties  of,  32. 
Protozoa,  190; 

classification  of,  198 ; 

habitat  of,  195 ; 

relation  to  disease,  196 ; 

use  as  food,  195. 
Pseudopodia,  193. 
Pteridophytes,  157. 
Ptomaines,  177. 
Ptyalin,  357. 
Pulmonates,  271. 
Pulse,  cause  of,  374. 
Pupa,  238,  239. 
Pylorus,  367. 


446 


INDEX 


Radiolarian,  198. 

Ray  flower,  44. 

Reflex  action,  nervous,  403. 

Regeneration,  defined,  215. 

Relation,  of  alcohol  to  disease,  412 ; 

of  bacteria  to  fermentation,  177  ; 

of  birds  and  reptiles,  310 ; 

of  bodily  heat  to  work,  392 ; 

of  breathing  to  exercise,  388 ; 

of  environment  to  diet,  336 ; 

of  flies  to  disease,  260,  261 ; 

of  Protozoa  to  disease,  196 ; 

of  spawning   to   economic   value, 
281; 

of  work  to  diet,  336. 
Rennin,  358. 
Reptiles,  study  of,  293. 
Reptilia,  characteristics  of,  296 ; 

classification  of,  297. 
Reproduction,  in  simple  plants,  199 ; 

in  simple  animals,   199 ; 
Respiration,  artificial,  389 ; 

effect  of  alcohol  on,  395 ; 

effect  of  tobacco  on,  396 ; 

excretion,  382 ; 

in  a  cell,  389,  390 ; 

in  birds,  301 ; 

in  crayfish,  224 ; 

in  fishes,  277 ; 

in  frog,  286 ; 

in  insects,  236 ; 

necessity  for,  382 ; 

nervous  control  of,  384 ; 

organs  of,  in  man,  382. 
Rest,  necessity  of,  405,  427. 
Rhizoids,  149,  153,  155. 
Ribs,  attachment  of,  327 ; 

in  respiration,  384. 
Rock  fern,  154. 
Rodents,  313. 
Root,  absorption  in,  89 ; 

effect  of  moisture  on,  85,  86 ; 

food  storage  in,  95 ; 

influence  of  gravity  upon,  84 ; 

passage  of  soil  water  in,  90 ; 

tip  of,  87. 
Root  form,  relation  of,  to  plant,  95. 
Root  hair,  88,  89. 
Root  pressure,  107. 
Root  system,  84. 


Roots,  adventitious,  96 ; 

air,  97  ; 

and  their  work,  84  ; 

different  from  stems,  115; 

parasitic,  97 ; 

prop,  of  corn,  96  ; 

water,  96. 
Roundworms,  217. 

Salamander,  spotted,  291. 

Saliva,  function  of,  356. 

Salmon  leaping  a  fall,  281. 

Sand  shark,  284. 

Sandworm,  216. 

Saprophytes,  149,  151. 

Sea  anemone,  208. 

Sea  lion,  313. 

Seasonal  variation  of  plumage,  309. 

Seaweeds,  144,  145. 

Seed  dispersal,  52,  53,  80. 

Seedling,  defined,  79. 

Seeds,  and  seedlings,  65 ; 

formation  of,  52 ; 

uses  of,  80 ; 

winged,  55,  56. 
Selective  absorption,  194. 
Selective  breeding,  316. 
Selective  planting,  81,  82. 
Self-control  vs.  appetite,  416. 
Self-pollination,  38. 
Sense  organs,  206,  286,  236. 
Senses,  in  birds,  302 ; 

in  fishes,  276 ; 

in  man,  406. 
Serum  of  blood,  367. 
Sexual  development  of  simple  ani- 
mal, 200. 
Sexual     reproduction,    in     animals, 
192,  194,  203,  208,  209,  215,  280, 
288; 

in  plants,  148,  150,  153,  154,  156. 
Shelf  fungus,  a  saprophyte,  173. 
Shipworm,  damage  by,  271. 
Shrimps,  227,  228. 
Skeleton,  and  muscles,  324 ; 

appendicular,  326,  327; 

axial,  326 ; 

of  birds,  300 ; 

of  dog,  325 ; 

of  fishes,  279 ; 


INDEX 


447 


Skeleton,  of  man,  326 ; 

structure  of,  ii25 ; 

uses  of,  325. 
Skeleton      building     in      Protozoa, 

198. 
Skin,  hygiene  of,  393 ; 

structure  of,  321. 
Skull,  of  dog.  313  ; 

of  man,  328; 

of  porcupine,  314. 
Sleep,  and  health,  421 ; 

necessity  of,  405. 
Smell,  organs  of,  407. 
Snail,  forest,  270. 
Snake,  garter,  294. 
Snakes,  value  of,  295 ; 

poisonous,  296. 
Soil,  composition  of,  21,  91 ; 

organic  matter  in,  92 ; 

water  in,  91,  92; 

weathering  of,  91. 
Soil  exhaustion,  prevention  of,  95. 
Solution,  Fehling's,  70 ; 

iodine,  66 ; 

nutrient,  93. 
Sound,  character  of,  409. 
Sparrow,  P]nglish,  307 ; 

white-throated,  309. 
Species,  defined,  157. 
Spermatophytes,  defined,  156,  157. 
Sperm  cell,  36,  199,  200,  208. 
Spiders,  245. 

Spinnerets  of  spiders,  245. 
Spiracles,  236. 
Spirogyra,  147. 
Sponge,  structure  of,  201. 
Sponges,  207. 
Sporangium,  149,  154. 
Spores,  149. 
Sporophyte,  a  parasite,  153 ; 

in  fern,  155 ; 

in  moss,  152. 
Squid,  270. 
Stamens,  34,  35. 
Starch,  in  bean,  66 ; 

non-osmosis  of,  106 ; 

to  grape  sugar,  71 ; 

test  for,  66. 
Starch  grains,  66. 
Starch  making,  and  milling,  123 ; 


Starch  making,  by  green  plants,  121 ; 

chemistry  of,  124 ; 

light  and  air  in,  122  ; 

rapidity  of,  125. 
Starfish,  272. 
Stem,  dicotyledonous,  101,  103 ; 

modified.  111; 

movement  of  fluid  in,  106,  107 ; 

monocotyledonous,  108; 

structure  and  work  of,  98. 
Stems,  112,  113. 
Stigma,  35,  69. 
Stimulants,  344. 
Stimuli,  response  to,  in  paramoecium, 

191. 
Stomach,  movement  of  walls  of,  358 ; 

nervous  control  of,  358 ; 

of  man,  363,  357. 
Stomata,  120,  128. 
Street  cleaning,  432. 
Streets,  condition  of,  431. 
Struggle  for  existence,  57. 
Sturgeon,  284. 
Style,  35. 
Suffocation,  389. 
Sugar,  consumption  of,  109; 

osmosis  of,  106. 
Sun,  a  source  of  energy,  119. 
Sundew,  130. 

Sunlight,  in  starch  making,  122. 
Sweat,  392. 
Sweat  glands,  321. 
Sweeping,  387. 
Swim  bladder,  278. 
Swimmerets,  222. 
Symbiosis,  187; 

between   plants   and   insects,   40, 
257; 

in  crabs,  230 ; 

in  lichens,  187 ; 

in  nitrogen-fixing  bacteria,  94. 
Systematic  botany,  157. 

Tadpoles,  of  frog,  290. 

Tail  of  birds,  function  of,  300. 

Tapeworms,  217. 

Taproot,  structure,  87. 

Tarantula,  245. 

Taste,  organs  of,  406. 

Taste  buds,  355,  406. 


448 


INDEX 


Teeth,  canine,  313 ; 

incisor,  314 ; 

kinds  of,  in  man,  355. 
Teleosts,  284. 
Temperature,  feeling  of,  406 ; 

in  germination,  76. 
Tentacles,  202. 
Thallophytes,  157. 
Thallus,  144. 

Thallus  plants,  divisions  of,  149. 
Thoracic  duct,  377. 
Thorax,  234 ; 

in  man,  327. 
Timber,  cutting  of,  138. 
Tissue,  28,  204,  322,  323. 
Tissues  of  human  body,  204. 
Toad,  common,  290. 
Tobacco,  effect  on  circulation,  381 ; 

effect  on  nervous  system,  349  ; 

effect  on  respiration,  396  ; 

use  of,  348. 
Tongue,  354. 
Tooth,  section  of,  355. 
Tortoise,  box,  294. 
Touch,  organs  of,  406. 
Tracheae,  235. 

Transpiration,  in  plants,  126,  127. 
Tree,  wounded  by  "cribbing,"  142. 
Trees,  city's  need  for,  141. 
Trilliums,  168. 
Trypanosomes,  197. 
Tuberculosis,  180; 

death  rate  from,  428,  429 ; 

fighting,  436. 
Turtles,  293. 
Tussock  moth,  263,  264. 
Typhoid  fever,  181 ; 

due  to  milk  supply,  434 ; 

due  to  water  supply,  433 ; 

fighting,  434. 

Underwing  moth,  250. 
Ungulates,  315. 
Urea,  393. 
Ureter,  390,  391. 
Urethra,  391. 
Uropod,  224. 

Vaccination,  431. 

Vacuole,  contractile,  191,  192,  193. 


Vacuole,  food,  191,  193. 
Veins,  370,  375. 
Ventilation,  need  of,  386 ; 

of  sleeping  rooms,  388 ; 

proper,  386,  387. 
Ventricle,  370. 
Venus's  flower  basket,  207. 
Venus's  flytrap,  131. 
Vermiform  appendix,  363. 
Vertebra,  326,  327. 
Vertebral  column,  326. 
Vertebrates,   compared  with  inver- 
tebrates, 274. 
Viceroy  butterfly,  251. 
Villus,  structure  of,  362. 
Virginia  deer,  315. 
Vorticella,  195. 

Walking  stick,  249. 
Warning  coloration,  251. 
Wasp,  solitary,  253. 
Water,  and  health,  420 ; 

and  typhoid,  433 ; 

composition  of,  20 ; 

factor  in  germination,  76 ; 

in  hygiene,  425 ; 

in  living  things,  23 ; 

necessity  of  pure,  432,  433. 
Water  storage,  in  leaves,  130 ; 

in  roots  and  stems.  111. 
Water   supply,   factor  in  modifica- 
tion, 160; 

regulated  by  forests,  133. 
Web,  spiders',  uses  and  forms,  246, 
Weed,  26. 

Wheat,  production  of,  59. 
Wheat  rust,  174. 
Wing,  of  moth,  237. 
Wings,  of  grasshopper,  234. 
Wood,  structure  of,  138 ; 

uses  of,  137. 
Worms,  harmful,  216 ; 

study  of  adaptations,  212. 

Xerophytes,  160,  161. 

Yeast,  171,  172. 

Yellow  fever,  caused  by  mosquito, 
259. 

Zygospore,  formation  of,  150. 


( 


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LIBRARY,  UNIVERSITY  OF  CALIFORNIA,  DAVIS 

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1946 


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Essentials  of  bloloar 


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